Introduction

CoolClient is a backdoor family attributed to the HoneyMyte APT group (also known as Mustang Panda) that has been used in their cyber-espionage campaigns targeting organizations across Asia and Russia. It supports such capabilities as keylogging, clipboard theft, credential harvesting, file management, system reconnaissance, and plugin-based extensions.

Since its first public disclosure by Sophos in 2022 and subsequent analysis by Trend Micro in 2023, CoolClient has continued to evolve. In 2025, we analyzed a newer variant that introduced clipboard theft and HTTP traffic interception for credential harvesting.

In late 2025 and 2026, our latest investigation reveal another major evolution. The newest CoolClient variant can deploy a signed kernel-mode driver as a Windows service and communicate with it through IOCTL requests. The driver enhances the malware’s stealth by hiding the CoolClient process, protecting related files and registry entries, and preventing them from being inspected or modified. The overall design is comparable to the kernel-mode enhancements previously observed in ToneShell, but the CoolClient driver exposes dedicated IOCTL handlers that allow the user-mode backdoor to communicate directly with the driver.

We have observed this updated CoolClient variant and its accompanying driver in intrusions across multiple countries in Asia, including Pakistan, Mongolia, and Myanmar.

Technical analysis

In the observed campaign targeting Myanmar, HoneyMyte used PlugX as the initial post-compromise implant to deploy the CoolClient components. Before deploying the malware, the actor added both a folder exclusion and a file exclusion to Microsoft Defender for the fake Windows Defender installation directory and the renamed sideloader executable (defender.exe).

wmic /Node:localhost /Namespace:\\Root\Microsoft\Windows\Defender Path MSFT_MpPreference call Add ExclusionPath="$programfiles\Microsoft\Windows Defender"
wmic /Node:localhost /Namespace:\\Root\Microsoft\Windows\Defender Path MSFT_MpPreference call Add ExclusionPath="$programfiles\Microsoft\Windows Defender\defender.exe"

The actor then created a fake Windows Defender installation directory, copied the CoolClient components into it, and renamed a legitimate Sangfor executable, usually named Sang.exe, to defender.exe to serve as the DLL sideloader.

xcopy "$programfiles\Windows Defender\*" "$programfiles\Microsoft\Windows Defender" /a /s /v /e /f

Persistence was established through a scheduled task that launched defender.exe with SYSTEM privileges during system startup.

schtasks /create /sc onstart /tn "\Microsoft\Windows\Windows Defender Advanced Threat Protection Service" /tr "\"$programfiles\Microsoft\Windows Defender\defender.exe\"" /ru "system" /F

When executed, defender.exe sideloads the malicious libngs.dll, initiating the CoolClient execution chain described in the following sections.

CoolClient components

Similar to previous variants, the latest CoolClient user-mode component follows a multi-stage execution chain, with each component performing a distinct role during execution.

Component	Description
defender.exe / Sang.exe	Legitimate Sangfor application abused for DLL sideloading
libsrapc.dll	Benign dependency required for the Sangfor application to execute normally
libngs.dll	First-stage loader that decrypts and loads the next stage into memory (First stage)
loadcert.ini	Encrypted DLL implementing the core CoolClient functionality, including command handling, process injection, driver deployment, and persistence (Second stage)
cert.ini	Final-stage implant responsible for C2 communication and backdoor functionality (Final stage)
time.ini	CoolCleint configuration file

Our previous CoolClient analysis focused primarily on the final-stage implant (main.dat), including its backdoor commands and plugin framework, while the first-stage loader (libngs.dll) and second-stage component (loader.dat) received only a brief overview. In the latest variant CoolClient, loader.dat and main.dat have been renamed to loadcert.ini and cert.ini, respectively. This article revisits those earlier stages, focusing on the second-stage component and the newly introduced kernel-mode driver that extends CoolClient with rootkit capabilities.

 

First stage: libngs.dll

Execution begins when the legitimate Sangfor application (defender.exe or Sang.exe) loads the malicious libngs.dll through DLL sideloading. As in previous CoolClient variants, the malware continues to abuse the same Sangfor application to execute its first-stage loader.

To make the DLL appear legitimate, libngs.dll exports numerous dummy functions. Each export simply calls OutputDebugStringA with its corresponding function name before immediately invoking ExitProcess, serving no functional purpose other than mimicking the expected export table of the legitimate DLL.

The actual malicious logic is executed from DllMain (DllEntryPoint). Although heavily obfuscated through control flow flattening and numerous unconditional jumps, the routine ultimately performs a straightforward task: loading, decrypting, and executing the encrypted second-stage DLL, loadcert.ini.

The loader resolves the required Windows APIs, reads loadcert.ini into memory, and decrypts it using a 0x32-byte repeating XOR keystream derived from a transformed seed value of 0xA4. After decryption, the DLL is loaded directly into memory, and execution is transferred to loadcert.ini.

Second stage: loadcert.ini (before synchost.exe injection)

The second-stage DLL, loadcert.ini, is responsible for preparing the execution environment before the malware transitions into its injected process. It first determines its execution context by checking whether the current module is synchost.exe.

If the DLL is running under the original sideloaded process (for example, Sang.exe), it performs the initial setup, including persistence, UAC bypass, registry modifications, and process injection.

If the DLL is already executing inside synchost.exe, it follows a different execution path that decrypts time.ini, deploys the kernel-mode driver, and loads the final-stage implant (cert.ini).

Command handler

The command handler remains largely unchanged from previous CoolClient variants, with one notable difference: the malware now injects into synchost.exe instead of write.exe.

Execution is controlled through three command-line parameters:

Parameter	Purpose
install	Performs the initial setup, including persistence, privilege checks, and preparation for the injected execution path.
work	Executes the primary second-stage functionality from the injected synchost.exe process, including driver deployment and third-stage loading.
passuac	Continues execution after privilege elevation.

If no parameter is supplied, the malware creates a new Sang.exe process with the install parameter using CreateProcessW.

Establishing AutoRun persistence

When executed with the install parameter, CoolClient creates an AutoRun entry under:

HKCU\Software\Microsoft\Windows\CurrentVersion\Run

The registry value, named goopdate, launches Sang.exe (or defender.exe, depending on the deployment) with the work parameter whenever the user logs on.

Process injection into synchost.exe

Upon establishing the AutoRun registry entry, CoolClient decrypts loadcert.ini using a 0x32-byte repeating XOR keystream derived from the hardcoded base key 0x4D.

The decrypted DLL is then injected into a newly created suspended instance of synchost.exe. The malware allocates memory in the target process, writes the decrypted payload, redirects the thread context to the injected code, resumes execution, and finally terminates the original process with ExitProcess.

From this point onward, execution continues entirely within synchost.exe, where the malware proceeds with kernel-mode driver deployment before loading the final-stage implant (cert.ini).

Service installation

When executed with the install parameter, CoolClient establishes an additional persistence mechanism by installing itself as a Windows service. Before doing so, it verifies that it has sufficient access to the Service Control Manager and that no 360 Total Security software processes (360sd.exe, zhudongfangyu.exe, or 360desktopservice64.exe) are running.

If both checks succeed, the malware decrypts time.ini to retrieve the service configuration, including the service name and description. It then checks whether the service media_updaten already exists. If found, the existing service is stopped and deleted before a new one is created.

The new service is configured to execute Sang.exe<.code> with the work parameter using CreateServiceA. The malware then starts the service by executing "sc start media_updaten" via WinExec.

Administrator privilege check

If the service installation path is not taken, CoolClient checks whether the current process is running with administrator privileges by verifying membership in the local Administrators group.

When administrative privileges are available, the malware relaunches itself with the passuac parameter before continuing with the remaining execution flow.

Elevated relaunch and UAC bypass

To continue execution with elevated privileges while concealing its true parent process, CoolClient implements an RPC-based process creation technique similar to the method described by Google Project Zero. The technique combines RPC process creation with parent process ID (PPID) spoofing to launch a new elevated instance of itself.

The malware first checks for the presence of escanmon.exe. If the process is running, it constructs the path to C:\Windows\System32\winver.exe and establishes a connection to the local ncalrpc endpoint (201ef99a-7fa0-444c-9399-19ba84f12a1a). It then invokes NdrAsyncClientCall to launch winver.exe through the RPC interface.

After winver.exe is created, CoolClient retrieves its debug object using NtQueryInformationProcess, detaches the debugger through NtRemoveProcessDebug, and terminates the process. The obtained debug object is later reused during the remainder of the UAC bypass routine.

Next, the malware repeats the same RPC-based process creation technique to launch computerdefaults.exe. It associates the previously obtained debug object with the current thread using DbgUiSetThreadDebugObject, waits for the resulting process creation event through WaitForDebugEvent, and duplicates the process handle using NtDuplicateObject, obtaining a handle with full access rights.

Finally, CoolClient relaunches itself as Sang.exe passuac using CreateProcessW with an extended startup attribute list. By configuring PROC_THREAD_ATTRIBUTE_PARENT_PROCESS through UpdateProcThreadAttribute, the duplicated process handle is assigned as the parent of the new process. As a result, the new Sang.exe passuac instance executes with an elevated context while appearing to have been spawned by the trusted Windows process instead of the original CoolClient process.

Second stage: loadcert.ini (Injected Execution)

After being injected into synchost.exe, loadcert.ini follows its injected execution path, where it deploys the kernel-mode driver and launches the final-stage implant (cert.ini). If administrative privileges are unavailable, the malware skips driver deployment and proceeds directly to the third-stage injection.

Kernel-Mode driver deployment

The deployment routine begins by decrypting time.ini. CoolClient then verifies that it has sufficient privileges to install a kernel-mode driver by checking for full access to the Service Control Manager (SCM) and the presence of SeTcbPrivilege.

If both conditions are met, CoolClient extracts an embedded LZMA-compressed driver from loadcert.ini, decompresses it, and writes it to disk as msagent.sys in the same directory as cert.ini, for example:

C:\Program Files\Microsoft\Windows Defender\msagent.sys

Next, the malware checks whether a service named msagent already exists. If present, the existing service is stopped and deleted before a new driver service is created and started, loading the kernel-mode component into the operating system.

Driver initialization

After the driver is loaded, CoolClient establishes communication with it by opening the device \\.\msagent using CreateFileW. The user-mode component then initializes the driver by issuing three DeviceIoControl requests.

IOCTL	Purpose
0x222120	Registers the current CoolClient process with the driver.
0x2221E0	Sends the configured C2 IPv4 address to the driver.
0x2220F0	Registers filesystem and registry paths that should be protected or hidden.

The first request (0x222120) registers the current CoolClient process as a trusted process within the driver. The request includes the process ID, an operation code, and a flag that marks the process as trusted, allowing it to interact with protected files, registry keys, and processes.

The second request (0x2221E0) passes the configured C2 IPv4 address extracted from time.ini.

Finally, 0x2220F0 registers the CoolClient installation directory (for example, C:\Program Files\Microsoft\Windows Defender\) together with the service registry path (\Registry\Machine\SYSTEM\CurrentControlSet\Services\media_updaten). These entries allow the driver to protect the malware’s files and registry objects from inspection, modification, and deletion.

As part of the initialization, CoolClient updates the HKLM\SYSTEM\RNG\Wid_H1deF5Dirs registry value by appending its installation directory if it is not already present. This registry value is later used by the driver when applying its hiding and protection mechanisms.

The implementation of these IOCTL handlers and the corresponding driver functionality are discussed in the msagent.sys section.

Cert.ini process injection

Once the driver has been initialized, CoolClient proceeds to launch the final-stage implant (cert.ini). Before creating the target process, the malware enumerates active WinStation sessions to identify a suitable interactive user session.

After selecting a session, CoolClient duplicates its access token, updates the session identifier, and creates a new synchost.exe process using CreateProcessAsUserA. The decrypted cert.ini DLL is then injected into the suspended process using the same memory allocation, thread context modification, and ResumeThread technique described earlier.

This marks the final transition in the execution chain, where the third-stage implant takes over C2 communication and the remaining backdoor functionality.

Msagent.sys driver

Analysis of the deployed kernel-mode driver reveals an embedded PDB path:

E:\work\南京实验室\2024项目\张雪杰云南m\研发\FTool\Tool\x64\Release\FTool.pdb

The path contains several notable strings, including “Nanjing Laboratory” (南京实验室) and “Zhang Xuejie Yunnan m” (张雪杰云南m), which likely refer to the driver’s development environment. However, our OSINT analysis did not identify any information linking these strings to a known organization, developer, or threat actor.

The driver is digitally signed with a certificate issued to "Nanjing Ranyi Technology Co., Ltd.", with serial number 3E 62 DC 5D 8D 61 2A 26 33 E7 6B DF D6 07 19 DD. The certificate was valid from August 2013 to September 2014.

We identified several older malicious drivers signed with the same certificate that were compiled around 2013. However, we found no evidence directly linking those samples to the CoolClient activity described in this article.

Driver configuration

During initialization, the driver loads its stealth configuration from the registry key \REGISTRY\MACHINE\SYSTEM\RNG. The configuration defines which system objects should be hidden or protected and controls the driver’s operating mode.

Two REG_DWORD values control the driver’s operating mode:

Registry Value	Default	Description
Hid_State	1	Enables the driver’s rootkit functionality.
Hid_StealthMode	0	Controls additional stealth features used by selected driver routines.

In addition, the driver loads several REG_MULTI_SZ values that define the objects to be hidden or protected.

Registry Value	Purpose
Wid_H1deF5Dirs	Directories to hide
Wid_H1deF5Files	Files to hide
Wid_H1deRegKeys	Registry keys to hide
Wid_H1deRegValues	Registry values to hide
Hid_IgnoredImages	Processes to ignore
Hid_ProtectedImages	Processes to protect

Together, these registry values determine which filesystem paths, registry objects, and processes are managed by the driver’s protection mechanisms.
After loading the configuration, the driver converts the registry entries into internal lookup structures that are shared across its various protection components.

These structures are later referenced by the filesystem minifilter, registry callback, process callback, object callback, image load callback, and IOCTL handlers to determine whether a file, registry object, or process should be hidden, protected, or ignored.

Preparation for process hiding

Next, the driver dynamically locates the ActiveProcessLinks (LIST_ENTRY) field within the EPROCESS structure instead of relying on hardcoded offsets. It first validates several predefined offsets and, if none match, performs a linear scan of the EPROCESS structure to identify the correct location. This approach allows the driver to remain compatible across different Windows versions, where the layout of EPROCESS may differ.

Once the correct offset has been identified, it is stored for later use by the process hiding routines. During process hiding and restoration, the driver uses IOCTLs 0x22219C and 0x2221A0 to unlink and relink entries in the Windows active process list, effectively hiding or restoring processes on demand.

Process, object, and image load callbacks

After preparing its process tracking structures, the driver initializes several AVL trees and populates them with configuration entries loaded from the registry, including Wid_H1deF5Dirs, Wid_H1deF5Files, Wid_H1deRegKeys, Wid_H1deRegValues, Hid_IgnoredImages, Hid_ProtectedImages, and Hid_HideImages.

These AVL trees provide efficient lookups for protected files, registry objects, and tracked processes, and are shared by the callback routines and IOCTL handlers.
The driver then registers three types of kernel callbacks that form the foundation of its protection and monitoring mechanisms:

• Object callbacks using ObRegisterCallbacks
• Process creation and termination callbacks using PsSetCreateProcessNotifyRoutineEx
• Image load callbacks using PsSetLoadImageNotifyRoutine

After registration, these callbacks maintain the driver’s internal tracking structures as processes, threads, and images are created or loaded.

Object callbacks

To protect selected processes, the driver registers object callbacks for process (PsProcessType) and thread (PsThreadType) objects using ObRegisterCallbacks with an altitude of 1203. These callbacks intercept requests to open process and thread handles. If the target process is protected, the driver reduces the access rights granted to the requesting process, preventing operations such as process termination, code injection, and other forms of process manipulation. In this sample, the protected process is the injected CoolClient code running inside synchost.exe.

Process and image load callbacks

The driver registers process creation and termination callbacks using PsSetCreateProcessNotifyRoutineEx, together with an image load callback via PsSetLoadImageNotifyRoutine.

When a process is created, its image name is compared against the configuration lists Hid_IgnoredImages, Hid_ProtectedImages, and Hid_HideImages. Matching processes are added to the driver’s internal tracking structures, allowing them to be protected, hidden, or managed through subsequent IOCTL requests. When a tracked process terminates, its entry is removed from the tracking structures.

The image load callback monitors modules loaded into tracked processes and updates the driver’s internal state to support subsequent protection and hiding operations.

To ensure that processes already running before the driver is initialized are also tracked, the driver performs a one-time enumeration of all active processes after registering the callbacks and adds any matching processes to the tracking structures.

MiniFilter registration

To protect files and directories, the driver registers a filesystem minifilter. During initialization, it creates internal path filter lists, loads the configured directory and file entries (Wid_H1deF5Dirs and Wid_H1deF5Files), and creates the required minifilter registry entries under HKLM\SYSTEM\CurrentControlSet\Services\msagent\Instances. To avoid altitude conflicts, the driver dynamically assigns a filter altitude and retries registration until a unique value is obtained.

The driver then activates the minifilter using FltRegisterFilter. The filter works together with the IOCTL interface, which dynamically adds, removes, or clears protected path entries (0x2220F0, 0x2220F4, and 0x2220F8). During filesystem operations, the minifilter compares accessed paths against its internal path lists and denies access to matching entries, effectively hiding protected files and directories from users and applications.

Registry callback registration

To protect registry keys and values, the driver registers a registry callback using CmRegisterCallbackEx with an altitude of 320000. During initialization, it creates separate lookup structures for protected registry keys and values, then populates them using the configured entries from Wid_H1deRegKeys and Wid_H1deRegValues.

Once registered, the callback intercepts registry operations and compares the target key or value against the protected entries. For enumeration requests, matching keys and values are removed from the results before they are returned to user mode, effectively hiding them from registry viewers. For direct access requests, such as opening, modifying, or deleting protected registry objects, the callback returns STATUS_ACCESS_DENIED, preventing the operation.

Before applying these restrictions, the driver verifies whether the requesting process is trusted. Processes registered through IOCTL 0x222120, including the CoolClient user-mode component, bypass the filtering logic and retain unrestricted access, while all other processes remain subject to the driver’s registry protection rules.

IOCTL command dispatcher

To communicate with the user-mode component, the driver creates a device object named \Device\ToolTool together with the symbolic link \DosDevices\ToolTool to allow the user-mode CoolClient component to communicate with the driver through DeviceIoControl requests.

The driver implements 33 IOCTL handlers, although the analyzed CoolClient sample uses only three during normal execution:

• 0x222120: registers the current CoolClient process with the driver.
• 0x2221E0: passes the configured C2 IPv4 address.
• 0x2220F0: registers filesystem and registry paths for protection.

The remaining IOCTL handlers were not invoked by the analyzed sample.

IOCTL	Handler	Functionality
0x222000	0x140001E04	Enable or disable the rootkit.
0x222004	0x1400020B0	Query the current rootkit state.
0x2220F0	0x140002320	●       Register protected filesystem or registry paths ●       Used by CoolClient to register its installation directory and service registry key.
0x2220F4	0x1400034DC	Remove a protected filesystem or registry path.
0x2220F8	0x140003464	Clear all protected filesystem and registry path entries.
0x222118	0x1400024B0	Register process or path protection entries.
0x22211C	0x140002A20	Query registered protection entries.
0x222120	0x140003794	Update process protection entries. Used by CoolClient to register itself as a trusted process.
0x222124	0x14000362C	Remove a protection entry.
0x222128	0x14000349C	Clear all process protection entries.
0x222130	0x14000265C	Register a protected process by PID.
0x222134	0x140010E88	Inject shellcode into a target process using NtCreateThreadEx.
0x222138	0x14000F498	Hide a kernel module by unlinking it from PsLoadedModuleList.
0x222144	0x14000270C	Delete a file.
0x222148	0x14000286C	Decrypt an embedded buffer and write it to disk.
0x22214C	0x1400027F4	Read and decrypt an encrypted file.
0x222168	0x140002780	Unmap the image section of a target process.
0x22216C	0x140013984	Terminate a process by PID.
0x222194	0x140011F50	Remove Protected Process Light (PPL) protection.
0x222198	0x140002940	Create or modify a registry value.
0x22219C	0x140010630	Hide a process by unlinking it from the active process list.
0x2221A0	0x140010670	Restore a previously hidden process.
0x2221A4	0x14000F8A0	Hide a module within a process.
0x2221A8	0x14000F954	Restore a hidden module.
0x2221AC	0x140016368	Enumerate and restore kernel notification callbacks.
0x2221B0	0x140016458	Disable or restore kernel notification callbacks.
0x2221B4	0x140012408	Manually load a secondary kernel driver.
0x2221B8	0x14001262C	Debug/test handler.
0x2221BC	0x1400165F6	Write to an arbitrary kernel address.
0x2221C0	0x14000BB00,  0x14000BB78	Enables deny-rootkit mode by registering image-load monitoring and enabling the patching logic.
0x2221C4	0x14000BB6C,  0x14000BB10	Disables deny-rootkit mode by clearing state and unregistering/removing the monitoring logic.
0x2221E0	0x1400126C0	Register a C2 IPv4 address.
0x2221E4	0x140012E50	Delete a C2 IPv4 address.

After initializing the IOCTL dispatcher, the driver releases the temporary configuration buffer that was previously loaded from \REGISTRY\MACHINE\SYSTEM\RNG.

Kernel module enumeration and hiding

To support kernel module hiding, the driver resolves the address of the non-exported kernel variable PsLoadedModuleList at runtime using MmGetSystemRoutineAddress. This global linked list maintains information about all loaded kernel modules and drivers, allowing the rootkit to enumerate and manipulate module entries.

This functionality is exposed through IOCTL 0x222138, which accepts a module name or path from the user-mode component. When a matching module is found, the driver locates the corresponding entry in PsLoadedModuleList and unlinks it by updating its Flink and Blink pointers. As a result, the hidden module no longer appears in standard kernel module enumeration routines.

Nsiproxy hooking and data filtering

The driver also hooks the Nsiproxy driver to filter network-related data returned to user mode. This functionality is connected to IOCTL 0x2221E0, which allows the user-mode component to register C2 IPv4 addresses with the driver.

To install the hook, the driver obtains a reference to \Driver\Nsiproxy using ObReferenceObjectByName and replaces one of the Nsiproxy handler pointers with its own filtering routine. The hook preserves the original handler and forwards execution after processing the returned data.

When the hooked routine processes network information, the driver compares the returned entries against its registered C2 address list. Matching IP addresses are removed before the data is returned to user mode, preventing applications that rely on Nsiproxy-provided network information from seeing the malware’s C2 addresses.

Finally, the driver registers a DriverUnload routine to release allocated resources when the driver is unloaded.

Victimology

The latest CoolClient variant continues to target organizations consistent with previously observed HoneyMyte activity. Based on our investigations, we identified victims in Myanmar, Mongolia, Pakistan, and Russia, including confirmed government entities.

Across the observed intrusions, CoolClient was consistently deployed as a secondary backdoor following a PlugX infection, indicating that HoneyMyte continues to use PlugX as its initial post-compromise implant before transitioning to CoolClient.

Attribution

Our analysis confirms that the investigated malware is a new CoolClient variant associated with the HoneyMyte threat group. While the overall execution flow remains consistent with previously documented CoolClient variants, this sample introduces a previously undocumented kernel-mode driver that significantly expands the malware’s stealth capabilities.

The deployment chain observed in this investigation is also consistent with previous HoneyMyte campaigns, in which PlugX serves as the initial foothold before CoolClient is deployed as a secondary backdoor, further reinforcing the attribution.

Conclusion

The latest CoolClient variant represents a significant evolution of the malware. Rather than operating solely as a user-mode backdoor with plugin support, it now deploys and communicates with a kernel-mode driver that extends its capabilities beyond earlier versions. Through this driver, CoolClient can hide and protect processes, files, and registry objects, as well as filter selected network information, making detection and analysis considerably more difficult.

HoneyMyte has previously introduced kernel-mode functionality in ToneShell. The addition of a kernel-mode driver to CoolClient suggests that the group continues to expand its use of rootkit capabilities to improve stealth, persistence, and defense evasion during post-compromise operations.

IOCs

2d7c8780e97409770a9d4f31c66c9d63 msagent.sys
9460E150E1981D5C165043520C5C12FE msagent.sys
9717F005C5FB98E08D2AD983D88F94EE libngs.dll
F518D8E5FE70D9090F6280C68A95998F libngs.dll
EB79558B037669792652A816E2C669DE ctxmui.dll

C:\Program Files\microsoft\windows defender\
C:\Program Files\windows media player\mediares\
C:\ProgramData\symantecdir\
C:\ProgramData\virtualstore\
C:\Windows\identitycrl\production\
C:\Windows\serviceprofiles\networkservice\
C:\Users\<user>\AppData\Local\viber24.8\
C:\Users\<user>\AppData\Roaming\dsassistant\
C:\Program Files\common files\microsoft shared\office14\
C:\programdata\msdn\

cloudtroe.giize[.]com
employers.theworkpc[.]com
freeread.casacam[.]net
us.lenovoappstore[.]com
sundanish.freeddns[.]org
torinarlabs.webredirect[.]org
news.dursamjbataar[.]org
video.dursamjbataar[.]org
black-popular[.]com
whatismybestthing[.]com

Introduction

During our research of activity affecting a diplomatic organization in Indonesia, we uncovered a previously undocumented malware family that we have named SharkLoader. What initially appeared to be an isolated case quickly expanded into a broader campaign as we identified additional SharkLoader infections across multiple countries and sectors.

Our investigation revealed that SharkLoader serves as a loader designed to deploy Cobalt Strike Beacon on compromised systems. We observed the threat actor deploying SharkLoader through exploitation of internet-facing applications, including Microsoft Exchange, Microsoft SharePoint, and Openfire Server, as well as through malware-based delivery mechanisms.

Beyond the diplomatic entity in Indonesia, we identified related activity targeting government organizations in Taiwan, software development companies across multiple countries, and entities in other sectors located in Hong Kong, Lebanon, Syria, Colombia, North Macedonia, Nepal, Serbia, and more. The observed victimology suggests a campaign with broad geographic reach and a diverse target set rather than a narrow focus on a specific industry or region.

For now, we are tracking this activity as StrikeShark. Although the operators utilize several open-source post-compromise tools associated with Chinese-speaking developers, we have not identified direct code reuse, infrastructure overlap, or operational similarity to confidently attribute the activity to any known APT or cybercrime group. As a result, attribution remains preliminary and the campaign’s ultimate objectives are still under research.

Initial infection

Our analysis of SharkLoader intrusions indicates that the threat actor employs multiple methods to gain initial access to victim environments. During our investigation, we observed two primary infection vectors: the exploitation of vulnerabilities in internet-facing applications and the deployment of custom dropper samples, some of which were disguised as legitimate software.

Exploitation of public-facing applications

In the incident affecting an Indonesian diplomatic entity, the threat actor exploited Microsoft Exchange vulnerabilities, including CVE-2021-26855 (ProxyLogon), to gain access to the target environment. Similar activity was observed in Taiwan, where software development organizations were compromised through exploitation of Openfire (CVE-2023-32315). In a separate incident affecting a Colombian organization, the threat actor exploited a GeoServer instance vulnerable to CVE-2024-36401.

Beyond these incidents, we identified additional exploitation activity targeting vulnerabilities in multiple internet-facing enterprise applications and network appliances including those listed below:

Remote Code Execution (RCE)

• Apache Shiro: CVE-2016-4437
• Hikvision Products: CVE-2021-36260
• Microsoft SharePoint: CVE-2021-27076
• Zimbra Collaboration Suite: CVE-2022-27925
• Microsoft Exchange Server: CVE-2022-41082
• F5 BIG-IP system: CVE-2023-46747
• Fortinet FortiOS: CVE-2024-21762
• React Server Components: CVE-2025-55182

Authentication Bypass

• Fortinet FortiOS: CVE-2022-40684
• Cisco IOS XE Web UI: CVE-2023-20198

As of the time of writing this article, we haven’t obtained the exploits the attackers used. However, based on the vulnerabilities observed across multiple attacks, we assess with medium confidence that the threat actor primarily relies on publicly available proof-of-concept (PoC) exploits to gain initial access. All the vulnerabilities identified during our investigation have publicly available exploit code, including PoCs hosted on GitHub and other open-source platforms, suggesting the actor leverages existing offensive resources rather than develops custom exploit capabilities. The victim profile also indicates that the activity is largely opportunistic, affecting organizations across various industries, regions, and technology environments without a clear focus on a specific target set. Also, one of the IP addresses associated with the C2 domain was also observed conducting internet-wide scanning activity, potentially aimed at identifying and exploiting vulnerable internet-facing systems at scale.

Following exploitation, the attacker established persistence on compromised servers through the deployment of webshells. Although we were unable to recover the webshell files, a series of commands whose execution we observed in our telemetry along with the detection records of webshells strongly indicate their use for post-exploitation activities.

One of the earliest observed actions involved copying the legitimate Windows application SystemSettings.exe to a new location before executing it.

cd C:\Windows\ImmersiveControlPanel\
copy SystemSettings.exe C:\ProgramData\
cd C:\ProgramData\
SystemSettings.exe

This application was later abused as part of a DLL sideloading chain used to launch SharkLoader, which in this scenario was hidden in the malicious SystemSettings.dll library. We suspect that this DLL along with malicious encrypted files, which we’ll describe further, was uploaded through the webshell to the same directory as SystemSettings.exe.

In another case involving the exploitation of CVE-2021-27076, the threat actor launched SystemSettings.exe triggering the subsequent SharkLoader sideloading chain from different directories on the system, which suggests renewed operational activity in the victim environment. In some of the cases, they used security product vendor names as the directory names, allegedly to appear legitimate.

cd C:\ProgramData\KasperskyLab\
dir
.\SystemSettings.exe
cd %APPDATA%
dir
cd kasperskylab
dir
.\SystemSettings.exe

Dropper-based distribution

In several observed cases, the threat actor distributed SharkLoader through custom dropper executables masquerading as legitimate software installers or applications such as Google Update and Cisco AnyConnect. However, the exact delivery mechanism used to distribute these droppers remains unknown.

The observed dropper filenames include:

• GoogleUpdateStepup.exe
• AnyConnect-win-4.10.04071-predeploy-k9exe
• AutoUpdate.exe
• 319-pfd-8001-reva_traitement biologique_master.zip

In one of the samples we analyzed, the threat actor used a legitimate Cisco AnyConnect VPN installer as a lure. The custom dropper extracted zlib-compressed data embedded within its resource section, decompressed it into an MSI package, and wrote the file to %APPDATA%\reports\AnyConnect-win-4.msi. The MSI package was a legitimate Cisco AnyConnect VPN installer, which was subsequently executed via the ShellExecuteW API, making the user believe the custom dropper was a legitimate application.

While the Cisco AnyConnect installer was decompressed and executed, SharkLoader components were silently dropped into directories in %APPDATA% different from %APPDATA%\reports\ in the background, executing the malware loader once the installation process completes.

In addition to installer-themed lures, several SharkLoader droppers use decoy PDF documents to persuade victims to open the malicious file. However, not all samples employ this technique, as some droppers function solely as a delivery mechanism for SharkLoader without presenting any lure content.

Among the samples analyzed, most droppers write the decoy PDF to a subdirectory named aswerf within the %TEMP% directory, while others save the document directly to %TEMP%.

Analysing the sample shows the PDF files are stored within the dropper’s resource section under the resource name TELEMETRY and are compressed with zlib. Upon execution, the dropper extracts and decompresses the embedded PDF, writes it to disk using the same filename as the dropper executable but with a PDF extension, and launches it via cmd.exe /c to display the decoy document to the victim.

The following are examples of PDF documents extracted and displayed by the droppers during the deployment of SharkLoader.

In one dropper sample, discovered on a machine located in Lebanon (MD5: 1F65544978B8EA0E745E573B8EE9684B), the dropper extracts and decompresses SystemSettings.dll from zlib-compressed data embedded within the binary and writes it to %APPDATA%\xwreg. It also extracts and decompresses DscCoreR.mui and SyncRest.dat from resources named VAULTSVCD and UMRDPRDAT, respectively, and writes them to the same directory.

The dropper then copies the legitimate SystemSettings.exe application from C:\Windows\ImmersiveControlPanel to the target location to facilitate DLL sideloading. Across other SharkLoader dropper samples analyzed, the malware components were observed being written to either %APPDATA%\xwreg or %APPDATA%\xgdf.

SharkLoader installation

SharkLoader is composed of multiple components that work together to load and execute the final implant, a Cobalt Strike Beacon.

Filename	Description
SystemSettings.exe	Legitimate Windows application abused for DLL side-loading of the malicious DLL SystemSettings.dll.
SystemSettings.dll	Main malicious SharkLoader DLL responsible for the core loader functionality.
DscCoreR.mui	An encrypted module that contains an embedded Cobalt Strike Beacon and the MinHook library. This module loads SyncRes.dat, installs a couple of API hooks, and executes the Beacon directly in memory.
SyncRes.dat	An encrypted DLL that is used to install multiple API hooks.

While the majority of SharkLoader samples analyzed rely on the sideloading of SystemSettings.dll, other variants leverage alternative DLL side-loading targets, including msedge.dll, PrintDialog.dll, and miracastview.dll, each of them leveraging a corresponding legitimate application.

Across the different variants examined, the encrypted modules were also observed using a variety of filenames, including:

GameInputInboxs32.mui
diagerr.xml
NtfsLog.etl
Ignored.Dat
VistaCompat.nls

The SharkLoader execution flow is as follows:

In the dropper-based infections, after deploying all required SharkLoader components, the dropper creates two scheduled tasks through the Windows Task Scheduler COM interfaces. Task names:

• OneDrive Standalone Update Task-S-1-5-21-4165425321-4153752593-2322023643-1000
• MicrosoftUpdateTaskUserS-1-5-32-2456537112-101246289-228944324-1000

Both tasks are configured to execute the copied SystemSettings.exe from the malware’s working directory (for example, %APPDATA%\xwreg or %APPDATA%\xgdf), triggering the side-loading of the malicious SharkLoader DLL.

The first scheduled task uses a time-based trigger that executes every five minutes, providing long-term persistence.

The second task is configured to execute every second, likely to ensure immediate execution of SharkLoader following deployment.

After a delay of approximately 1.5 seconds, the dropper removes the second scheduled task by using the Task Scheduler COM interfaces, leaving the first task in place to maintain persistence on the system.

SharkLoader DLL – Main implant

For the detailed analysis of the infection chain, we’ll focus on the SharkLoader components deployed by a malicious dropper named 一种异常状况的截图（包括操作系统和输入法版本）.pdf.exe (MD5: 24FCEBDEECBA65004FDB0923763D74FD), which was identified in a campaign targeting a government entity in Taiwan.

Filename	MD5
SystemSettings.exe	D98F568496512E4F98670C61C97CB07A
SystemSettings.dll	AA3086BE652C8B20B0B29B2730D57119
DscCoreR.mui	A514D1BB62D7916475946FE7C07AC0AA
SyncRest.dat	9CBD560F820C95D7C38342CD558CB5C6

“PerfectDLL Hijacking” technique

Once the malicious DLL is loaded, SharkLoader implements a technique commonly referred to as “Perfect DLL Hijacking” and originally described by a security researcher named Elliot Killick on his blog. The purpose of this technique is to bypass the Windows loader lock and safely create a malicious thread via the CreateThread API without risking a deadlock.

According to Microsoft’s Dynamic-Link Library Best Practices, the Windows loader holds a synchronization object known as the “loader lock” while executing the DllMain function. This mechanism ensures that only one thread can perform DLL loading and initialization operations within a process at any given time. As a result, invoking APIs such as CreateThread or LoadLibrary from within DllMain can lead to deadlocks because the loader lock remains held throughout the execution of the function.

To avoid this issue, SharkLoader manipulates the process’s internal loader state to release the loader lock before invoking CreateThread from the DllMain execution path. By doing so, it attempts to execute its malicious code without triggering the loader-related deadlocks that can occur when threads are created while the loader lock remains held.

Based on the code, SharkLoader first resolves the addresses of several undocumented loader structures within ntdll.dll, including:

1. LdrpLoaderLock: the critical section object used by the Windows loader to synchronize module loading and initialization operations
2. LdrpWorkInProgress: an internal loader state variable that tracks whether module initialization is currently in progress

After locating these structures, SharkLoader forcefully releases the loader lock by invoking LeaveCriticalSection on LdrpLoaderLock. It then decrements the value of LdrpWorkInProgress with InterlockedDecrement64, effectively marking the initialization process as complete.

Finally, the malware signals the loader completion event via SetEvent before creating a new thread to execute its malicious functionality. As a result, these actions manipulate the loader’s internal state and cause Windows to treat the DLL initialization process as having completed successfully. This allows SharkLoader to continue execution after forcefully releasing the loader lock, despite still operating from within the DllMain execution path.

Decryption and loading of >DscCoreR.mui

As shown in the previous section, the loader creates a new thread after escaping the Windows loader lock. This thread subsequently spawns a second thread responsible for decrypting and reflectively loading the encrypted file, DscCoreR.mui.

The routine first reads the encrypted file into memory and extracts the first 16 bytes to use as the Blowfish decryption key. It then initializes the Blowfish cipher by using custom P-array and S-box constants embedded in the loader and decrypts the file in ECB mode with the extracted key. Once decryption is complete, the resulting PE file is reflectively loaded into memory and executed without being written to disk.

The decrypted DscCoreR.mui file is a packed PE file with its MZ header removed, likely as an anti-analysis measure. After decryption, SharkLoader processes the PE image by parsing its headers, allocating memory for the image, mapping its sections, applying relocations, resolving imported functions, and setting the appropriate memory protections. Once the in-memory PE loading process is complete, the main loader, SystemSettings.dll, transfers execution to the entry point of the mapped image, which contains the packer stub.

The stub then unpacks the protected code, invokes the DLL’s DllMain function, and returns execution to SystemSettings.dll. Finally, SystemSettings.dll calls the exported function SetUserProcessPriorityBoost from the mapped DLL, triggering execution of the fully unpacked next-stage DLL.

DscCoreR.mui and SyncRes.dat DLLs

Within the decrypted and unpacked DscCoreR.mui code, the malware proceeds to load and decrypt a second encrypted file, SyncRes.dat, before reflectively loading the resulting DLL into memory.

The mapped DLL installs multiple API hooks by using Microsoft Detours, which will be discussed in the next section.

After mapping and loading SyncRes.dat for API hooks, the DscCoreR.mui performs installation of the Vectored Exception Handler (VEH) and then creates a thread in a suspended state that is later used to execute the Cobalt Strike Beacon shellcode. Additionally, to facilitate additional API hooks, it decompresses and loads the MinHook library and uses it to install hooks on the VirtualAlloc and Sleep APIs.

The DscCoreR.mui then decompresses the Cobalt Strike Beacon shellcode into the memory region associated with the suspended thread and then the suspended thread is resumed, resulting in execution of the beacon.

Decryption and loading of SyncRes.dat

To decrypt SyncRes.dat, the malware extracts a 16-byte AES-128 key and a 16-byte initialization vector (IV) directly from the file itself. The first 16 bytes of the file contain the AES key, while the subsequent 16 bytes contain the IV. The remaining file content consists of AES-encrypted data, which is decrypted using the extracted key and IV. Once decrypted, the resulting data reveals a PE image with its MZ header removed, similar to DscCoreR.mui.

Similar to the decrypted DscCoreR.mui module, the decrypted SyncRes.dat file is also protected by an unknown custom packer. After decryption, the loader reflectively loads the PE image before transferring execution to the module’s entry point.

The entry point contains a packer stub responsible for unpacking the protected code in memory. Once the unpacking routine is complete, the malware invokes a specific exported function named StartEngineData, which serves as the primary execution routine of the third-stage DLL.

Before continuing with the DscCoreR.mui analysis, we will first discuss SyncRes.dat.

SyncRes.dat decrypted DLL: Multiple API hooks

The decrypted and unpacked SyncRes.dat DLL is primarily responsible for installing multiple Windows API hooks by using the Microsoft Detours library. After attaching all detour hooks, it calls DetourTransactionCommitEx to apply them in one commit.

The following table lists the hooked Windows APIs and their corresponding hook handler functions.

Hooked Windows APIs	Detour function description
CreateProcessA	Saves all original CreateProcessA parameters for use in the parent process (PPID) spoofing routine. Creates a new thread that executes the process creation routine responsible for PPID spoofing. Falls back to the original CreateProcessA if the thread creation fails. Identifies an svchost.exe process that has the same security context as the current SharkLoader process. Builds an extended startup attribute list to set the selected svchost.exe as the spoofed parent. Calls the original CreateProcessA with the modified parent attribute. As a result, any new process created by the current process (primarily from the Cobalt Strike beacon) is spawned under svchost.exe instead of the current module process.
CreateProcessW	Saves all original CreateProcessW parameters for use in the PPID spoofing routine, which is executed through an APC-based mechanism rather than a dedicated thread compared to the CreateProcessA API hook. Schedules a delayed process creation (10 microseconds) through APC execution using CreateWaitableTimerW and SleepEx. The timer callback performs the svchost.exe PPID spoofing logic, similar to the CreateProcessA spoofing routine. As a result, new processes created via CreateProcessW by the current process (primarily from the Cobalt Strike beacon) are launched under svchost.exe through an APC-based execution mechanism
OpenProcessToken	Once hooked, the malware initializes jitasm to construct a direct syscall stub for NtOpenProcessToken at runtime. Invokes NtOpenProcessToken through the constructed direct syscall stub, redirecting the original API (OpenProcessToken) call flow.
AdjustTokenPrivileges	Redirects the API call to a direct NtAdjustPrivilegesToken syscall stub constructed by jitasm.
OpenProcess	Redirects the API call to a direct NtOpenProcess syscall stub constructed by jitasm.
WriteProcessMemory	Redirects the API call to a direct NtWriteVirtualMemory syscall stub constructed by jitasm.
NtCreateUserProcess	Redirects the API call to a direct NtCreateUserProcess syscall stub constructed by jitasm.
LoadLibraryA	Redirects the API call to a function that resolves LdrLoadDll API using a ROR13-based API hashing algorithm. Uses the original parameters to invoke LdrLoadDll directly. If LdrLoadDll resolution or invocation fails, uses CreateTimerQueue and CreateTimerQueueTimer to schedule a 10-millisecond delayed execution of the original LoadLibraryA, with CreateEventW used for synchronization.
GetModuleHandleA	Redirects the API call to a custom function that resolves the module base address through the following steps: Enumerates loaded modules within the current process using CreateToolhelp32Snapshot, Module32FirstW, and Module32NextW. Compares each enumerated module name with the module name provided in the API parameter. Returns the module base address if a match is found. Falls back to the original GetModuleHandleA API if the custom resolution routine fails.
GetModuleHandleW	Similar approach to the GetModuleHandleA API hooks above.
GetProcAddress	The original GetProcAddress parameters are passed to the hook handler. The hook handler computes a Murmur32 hash of the requested function name. The hook handler parses the module’s PE structure and locates the export table. Each exported function name is hashed using the same Murmur32 algorithm and compared against the previously generated hash. If a hash match is found, the corresponding function address is returned. If no match is found, the call falls back to the original GetProcAddress.
LoadLibraryExA	The hook handler redirects the API call to its original address. In short, the hooked LoadLibraryExA calls the original LoadLibraryExA function.
VirtualAllocEx	Redirects the API call to a direct NtAllocateVirtualMemory syscall stub constructed by jitasm.
VirtualProtectEx	Redirects the API call to a direct NtProtectVirtualMemory syscall stub constructed by jitasm.
VirtualProtect	Redirects the API call to a direct NtProtectVirtualMemory syscall stub constructed by jitasm.
ResumeThread	Redirects the API call to a direct NtResumeThread syscall stub constructed by jitasm.
GetThreadContext	Redirects the API call to a direct NtGetContextThread syscall stub constructed by jitasm.
OpenThread	Redirects the API call to a direct NtOpenThread syscall stub constructed by jitasm.
NtCreateThread	Redirects the API call to a direct NtCreateThread syscall stub constructed by jitasm.
NtCreateThreadEx	Redirects the API call to a direct NtCreateThreadEx syscall stub constructed by jitasm.
NtQueueApcThread	Redirects the API call to a direct NtQueueApcThread syscall stub constructed by jitasm.
NtQueueApcThreadEx	Redirects the API call to a direct NtQueueApcThreadEx syscall stub constructed by jitasm.
ExpandEnvironmentStringsA	The detour redirects the API to a custom function that creates a new thread. That thread executes a routine that calls the ExpandEnvironmentStringsA API.
CreateFileMappingA	The detour redirects the API call to a custom function that creates a new thread. Within the thread, it initializes thread-pool and timer objects, sets a threadpool timer for 10 ms and a waitable timer for 0.1 ms, then calls CreateFileMappingNumaA. If thread creation fails, CreateFileMappingNumaA is called directly without creating a thread.
MapViewOfFile	The detour redirects the API call to a custom function that creates a new thread. The thread runs a similar thread-pool and timer setup to the previous function, resolves MapViewOfFileEx via GetProcAddress, calls it with zeroed arguments, and stores the return value.
UnmapViewOfFile	The detour redirects the API to a function that tries to run the unmap (same API) in a new thread. The thread creates an event and timer queue, schedules a callback after 10 ms to call UnmapViewOfFile and signal the event, then waits and cleans up. If thread creation fails, it calls UnmapViewOfFile directly.
NtMapViewOfSectionEx	Redirects the API call to a direct NtMapViewOfSectionEx syscall stub constructed by jitasm.
NtCreateNamedPipeFile	Redirects the API call to a direct NtCreateNamedPipeFile syscall stub constructed by jitasm.
NtReadFile	Redirects the API call to a direct NtReadFile syscall stub constructed by jitasm.
NtWriteFile	Redirects the API call to a direct NtWriteFile syscall stub constructed by jitasm.
EtwEventWrite	The detour redirects EtwEventWrite to a stub that always returns 1, which prevents ETW logging.
EventWriteEx	The detour redirects EventWriteEx to a function that always returns 0, which prevents ETW logging.
EventWrite	The detour redirects EventWrite to a function that always returns 0, which prevents ETW logging.

Upon completing the installation of API hooks via the decrypted SyncRes.dat, the DscCoreR.mui DLL proceeds with the remaining functions, which are discussed below.

VEH registration and access violation handling

Following the installation of the API hooks, the malware registers a Vectored Exception Handler (VEH) to monitor exceptions generated during runtime. The handler specifically checks for access violation exceptions (0xC0000005). When such an exception occurs, it retrieves the faulting memory address from the exception record and calls VirtualProtect to restore read, write, and execute (RWX) permissions to the corresponding memory page before resuming execution.

During our analysis, no access violations were observed. It is possible that this mechanism is intended to handle access violations that may occur under specific runtime conditions.

Thread creation for Cobalt Strike Beacon execution

The malware creates a new thread in a suspended state that is intended to execute the Cobalt Strike Beacon shellcode. The thread entry point is configured to point to a memory buffer that will later contain the beacon shellcode.

At this stage, the buffer does not yet contain the actual Cobalt Strike Beacon shellcode. Instead, the thread is created in a suspended state so that the malware can prepare and inject the shellcode into the buffer before execution. Once the beacon payload has been written into the buffer, the malware resumes the suspended thread using the ResumeThread API, which triggers the execution of the Cobalt Strike beacon.

MinHook DLL, API hooking, and Cobalt Strike beacon

After creating the suspended thread for beacon execution, the malware decompresses a zlib-compressed MinHook PE file embedded within DscCoreR.mui. The MinHook library is used to install API hooks for the VirtualAlloc and Sleep functions. Once the MinHook DLL is decompressed and loaded into memory, the malware resolves the exported functions MH_Initialize and MH_CreateHook, which are then used to install hooks on the VirtualAlloc and Sleep APIs.

After the hooks are installed, the malware invokes a function that decompresses a zlib-compressed Cobalt Strike Beacon shellcode embedded within the malware. The function first decompresses the shellcode into a temporary buffer and then allocates executable memory using VirtualAlloc with RWX permissions. The decompressed beacon is subsequently copied into the allocated memory region.

Because the VirtualAlloc API has already been hooked at this stage, the hook handler captures the address and size of the allocated memory used to store the beacon shellcode. The hook records the addresses and sizes of the first three successful memory allocations and stores these values in global variables to track specific memory regions allocated during execution. These tracked regions are associated with memory buffers used by the Cobalt Strike Beacon during runtime.

The second hook, on the Sleep API, is used when Cobalt Strike Beacon calls Sleep, such as during beacon sleep intervals. It temporarily modifies the memory protection of the tracked allocation regions by using VirtualProtect, changing their protection to PAGE_READWRITE (RW) before invoking the original Sleep function. After the sleep period ends, the malware restores the memory protection of those regions to PAGE_EXECUTE_READWRITE (RWX). This behavior suggests that the malware developer implemented this mechanism to evade memory scanning techniques that identify executable (RWX) code regions in memory.

Finally, after the API hooks are installed and the Cobalt Strike Beacon shellcode has been written to the thread buffer, the malware calls the ResumeThread API to resume the suspended thread and begin execution of the beacon.

Persistence mechanism

While the analyzed SharkLoader implant does not contain a built-in persistence mechanism especially when it comes to cases when it is dropped after the exploitation of a public-facing application, our investigations revealed that the threat actor employs several techniques to maintain access to compromised systems.

Registry Run key: In the incident that affected an organization in Hong Kong, the attacker manually created a registry Run key to launch SystemSettings.exe upon user logon. The following command was used:

reg add HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run /v "MFUpdate" /t REG_SZ /d "$appdata\Identities\SystemSettings.exe" /f

This technique allows the malware to automatically execute whenever the user logs in, ensuring persistent access.

Scheduled task: In the separate compromise that affected a diplomatic government entity in Indonesia, the attacker established persistence through a scheduled task configured to execute SharkLoader daily. The task, named "\Microsoft\Windows\Edge\Edgeupdate", was configured to run C:\ADriveLogs_Logs\SystemSettings.exe by using the following command:

Schtasks /create /s /u "" /p "" /ru "SYSTEM" /tn "\Microsoft\Windows\Edge\Edgeupdate" /sc DAILY /tr "C:\ADriveLogs_Logs\SystemSettings.exe /F"

Running the task with SYSTEM privileges ensures that SharkLoader executes even if no user is logged in.

Post-compromise activity

Following initial compromise and persistence, the attacker engaged in extensive reconnaissance and credential theft activities.

System information enumeration: The attacker initially gathered basic system information by using the following commands:

systeminfo
ipconfig /all
tasklist /svc

Post-exploitation tools: Our analysis revealed the use of several third-party post-exploitation tools, most of which are open-source and developed by Chinese-speaking developers. These tools included:

Tool name	Description
FScan	Network scanner tool with vulnerability exploitation modules
Searchall	Sensitive information search tool
Pillager	Information gathering tool

We also detected the use of SharpGPOAbuse by the threat actor, a tool designed to modify Group Policy Objects within Active Directory environments.

Active Directory enumeration: In the compromise affecting a diplomatic government entity in Indonesia, the attacker used both Cobalt Strike and a webshell to enumerate the internal Active Directory environment. They executed a series of commands to gather information about the network, users, and groups:

• Network information:
  

  ping -n
  netstat -ano
  arp -a
  net share

• User and group information:
  

  query user
  nslookup
  quser
  net group /domain

• Specific group membership:
  

  powershell "Get-ADGroupMember -Identity "" -Recursive | Select-Object Name, ObjectClass"
  dsquery group -name "" | dsget group -members -expand | dsget user -samid -display -email"
  powershell "Get-ADGroupMember -Identity "" -Recursive | Where-Object { $_.ObjectClass -eq "computer" } | Select-Object Name, SamAccountName"
  powershell -exec bypass -c "Get-ADUser -Filter * -Prop * | select sAMAccountName
  net group "Domain Controllers" /domain
  net group "Enterprise Admins" /domain
  net group "Organization Management" /domain
  net group "domain admins" /domain

• Process enumeration:
  

  tasklist /SVC | findstr $selfname.exe

• Directory listing:

dir \\c$
dir \\c$\inetpub
dir \\c$\inetpub\custerr
dir \\c$\inetpub\wwwroot\

Credential dumping: The attacker also attempted to dump credentials from the compromised machine by targeting both the LSASS process and the NTDS database file. The following commands were observed:

ntdsutil "ac i ntds" "ifm" "create full $temp" q q
Procdump64.exe -accepteula -ma lsass.exe $temp\lsass.dmp

Dumping the LSASS process allows the attacker to extract in-memory credentials, while accessing the NTDS database enables retrieval of Active Directory account password hashes. This combination of techniques allows the attacker to obtain privileged credentials for lateral movement, privilege escalation, and deeper compromise.

Victimology

The victimology observed in this campaign shows a combination of strategic and opportunistic characteristics. Confirmed victims include government-related entities, such as the ministry in Taiwan and the diplomatic organization in Indonesia, as well as software development companies in Taiwan, Lebanon, and Syria. Additional affected organizations were identified in Hong Kong, Colombia, Macedonia, Nepal, and Serbia.

Targeting of government and software development organizations may indicate a cyber-espionage objective, although our confidence remains low due to the limited post-compromise activity observed, which primarily consisted of credential access, system reconnaissance, and lateral movement. The compromise of government and software development organizations could indicate an interest in gathering political intelligence or intellectual property.

At the same time, the use of SharkLoader and Cobalt Strike, alongside the exploitation of public-facing applications and malicious installers and droppers, suggests the attacker may also be opportunistically targeting vulnerable systems. The absence of clear evidence of data exfiltration thus far does not exclude this possibility, as Cobalt Strike’s file operation and data exfiltration modules could be employed at a later stage.

Although the full scope of the campaign is not yet known, the combination of targeted and opportunistic activity suggests it should continue to be closely monitored.

Attribution

Our investigation reveals no code or infrastructure overlap linking SharkLoader to any existing threat actor at this time. The TTPs employed during the operation also do not align with those of known actors.

However, analysis of the post-exploitation open-source tools used during the campaign revealed that several reconnaissance tools, including FScan, Searchall, and Pillager, were developed by individuals identified as Chinese speaking developers on GitHub.

We assess StrikeShark to be a Chinese-speaking threat actor with low confidence. This assessment is based on limited indicators and should be considered preliminary. Further investigation is required to characterize this cluster more fully, and the possibility remains that other actors may also be utilizing these tools.

Conclusion

Our investigation discovered a previously undocumented intrusion cluster that we are tracking as StrikeShark. The StrikeShark campaign represents a sophisticated malware threat to entities worldwide. The use of SharkLoader to deploy Cobalt Strike, coupled with API hook installation to evade detection, demonstrates a significant level of technical expertise. The campaign’s broad targeting across sectors and geographic regions suggests a potential focus on espionage or information gathering. While the precise objectives remain under investigation, the combination of targeting government entities and software developers warrants heightened vigilance.

Given that our visibility is limited to incidents observed through Kaspersky telemetry, we suspect the actual number of compromises may be significantly higher and extend beyond these victims as the threat actor actively used several exploitations of public facing application.

Indicators of compromise

Additional information about this activity, including indicators of compromise, is available to customers of the Kaspersky Intelligence Reporting Service. If you are interested, please contact intelreports@kaspersky.com.

C559CC68986933200FD5D9E4388E2F58                    Installer
B3352B42432DEDC4A519F011DC8B5D5A                  Dropper
24FCEBDEECBA65004FDB0923763D74FD                  Dropper
9C872A0D5D5A38950E8B9AC9B488BE3F                  SharkLoader DLL
AA3086BE652C8B20B0B29B2730D57119                   SharkLoader DLL
A514D1BB62D7916475946FE7C07AC0AA                  Encrypted file
9CBD560F820C95D7C38342CD558CB5C6                  Encrypted file
connect-microsoft[.]com
ms-record[.]com
ms-record[.]top
ms-tray[.]top

In June 2026, we observed a malware campaign distributing malicious VBScript files through direct messages in WhatsApp. The campaign affected users across multiple countries and territories, including Malaysia, Brazil, India, Mexico, Singapore, UK, Spain, Taiwan, Australia, Russia and Vietnam, with the highest number of victims observed in Malaysia. At the time of writing this article, the campaign is still active.

Analysis shows that the campaign primarily targets users of WhatsApp Desktop and WhatsApp Web. The threat actor uses deceptive file names masquerading as business and financial documents to persuade recipients to download and execute the attachment. Once executed, the VBScript initiates a multi-stage infection chain that ultimately results in the installation of legitimate Remote Monitoring and Management (RMM) software, enabling remote access to the victim’s system.

We came across a number of social media posts reporting that the malware was being distributed by the users’ contacts. The messages contained only the malicious attachment and did not include any accompanying text. One account sent the same attachment to multiple contacts from their list.

Based on evidence collected from multiple victims through social media reports and submitted samples, we can conclude that the threat actor had gained access to several WhatsApp accounts and used them to distribute the malicious VBScript files to contacts on the compromised users’ contact lists. At the time of writing, the exact method used to compromise these WhatsApp accounts remains unknown.

Social engineering through financial-themed file names

Analysis of the samples revealed that the threat actor relied heavily on social engineering through the use of deceptive file names designed to appear as legitimate business and financial documents. The file names frequently referenced invoices, account statements, debt notices, payment records, and bank statements.
Examples of file names include:

• Financial Reports.vbs
• Debt confirmation.vbs
• Statement of Debt(30K).vbs
• Outstanding Payment List.vbs
• Account Statement.vbs
• Debt Statement.vbs
• Billing Statement (2).vbs
• Promissory_Note(b).vbs

Several file names were also localized into different languages, including Portuguese, French, German, and Malay. Examples include:

• Extrato de Conciliação.vbs
• Aviso de dívida.vbs
• Le formulaire de demande le plus récent.vbs
• Bitte füllen Sie das Formular für Umsatzsteuer-Nullsatz-Verkäufe aus.vbs
• Penyata bank.vbs
• Sila semak bil anda.vbs

The use of multiple languages further suggests that the campaign may be targeting victims across different geographic regions.

In addition, the VBScript samples contain extensive comments and metadata intended to mimic legitimate Microsoft Windows Update components. Many of these comments are written in Chinese and include references to Windows Update modules, certificate validation, system integrity checks, and deployment-related functionality. The screenshot below shows an example of the Windows Update–themed comments and Chinese-language annotations embedded within one of the analyzed scripts.

Delivery of the initial VBScript file

Analysis of telemetry collected from the systems where the malware was executed, conducted together with the dynamic analysis of the sample, showed that the VBScript is launched through Windows Script Host (WScript.exe), which subsequently retrieves and executes additional VBScript components required for the later stages of the attack.

Two user interactions are needed to initiate the infection chain. When the user first clicks the attachment in either WhatsApp Desktop or WhatsApp web, it is downloaded to their machine. To launch the app, they need to open it.

In WhatsApp Desktop, the malware is executed directly within the application by clicking the file icon after downloading it or by choosing the “Open” option in the chat. The process tree analysis shows that WScript.exe is spawned by WhatsApp.Root.exe. The executed script was observed within WhatsApp Desktop’s attachment storage directory, with the following command line:

"C:\Windows\System32\WScript.exe" "C:\Users\<username>\AppData\Local\Packages\5319275A.WhatsAppDesktop_cv1g1gvanyjgm\LocalState\Sessions\<session_identifier>\Transfers\<YYYY-MM>\financial reports(s).vbs"

This process relationship confirms that the malicious VBScript was executed directly from the WhatsApp Desktop client.

In contrast, when the attachment is accessed through WhatsApp Web, to launch the malware, the user should open the downloaded file from the Downloads folder or through the browser’s download history. In the first case, the malware’s parent process will be explorer.exe, while in the second, it will be executed by the browser where the web app was opened.

Technical analysis

Stage 1: Initial VBScript execution

The first stage of the infection chain is a VBS or VBE file delivered through WhatsApp. Although multiple variants of the scripts were observed, their core functionality remains consistent: the script creates a working directory under C:\Users\Public\Documents\, downloads two additional VBScript payloads from a remote infrastructure, and executes them using Windows Script Host.

Across the observed variants, the working directory is created using randomized names such as Temp_<random> or MSUpdate_<random>. Some variants also configure the directory and downloaded files with hidden and system attributes, likely to reduce visibility to the user during execution.

The scripts employ several obfuscation techniques, including string concatenation, encoded VBScript, randomized variable names, and large amounts of junk content. One notable variant employs even heavier obfuscation than the other samples. The script reconstructs object names, file paths, utilities, and URLs through character-by-character string concatenation.

Several variants copy curl.exe and bitsadmin.exe into the working directory and rename them using DLL-like filenames before downloading additional VBS files.

The downloaded files are commonly staged using misleading file extensions before execution. For example, some variants download files using PDF or TXT extensions and then change them to VBS before launching them with wscript.exe. Other variants download the secondary VBScript payloads directly.

Despite differences in infrastructure, file names, and obfuscation methods, all observed variants ultimately perform the same function: downloading and executing two secondary VBScript payloads that continue the infection chain.

Stage 2: Execution of secondary VBScript payloads

Following execution, the Stage 1 VBScript downloads and launches two additional VBScript files from attacker-controlled infrastructure. One script attempts to modify Windows User Account Control (UAC) settings, while the other downloads and executes a ZIP archive containing the installation package for a RMM software.

VBS script 1: UAC configuration modification

First Stage 2 scripts were observed attempting to modify Windows      UAC     behavior.

As shown in the figure above, the script repeatedly executes an elevated registry modification command targeting the following registry key:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\ConsentPromptBehaviorAdmin

The command is launched using the ShellExecute method with the runas verb, causing Windows to request administrative privileges before the registry change can be applied. Its goal is to set the ConsentPromptBehaviorAdmin registry key value to 0, thus enabling administrative actions without displaying a consent prompt to the user. The script attempts to apply this registry change in a loop with short delays between executions, likely to increase the chances that the setting will be successfully modified if administrative privileges are granted by the victim.

VBS script 2: ZIP download and script execution

The second VBS script downloads a ZIP file, extracts it and executes a script to start the RMM installation.

Similar to the Stage 1 downloader, the Stage 2 downloader creates its own working directory under C:\Users\Public\Documents\, commonly using randomized folder names such as Sys<random>, Data<random>, or a random numeric value. In most cases, the hidden attribute is assigned to this folder. The script then downloads a ZIP archive from attacker-controlled infrastructure, extracts its contents, and executes an embedded setup1.vbs script.

Similar to the Stage 1 downloader, the variants leverage multiple download mechanisms, including curl, bitsadmin, certutil, PowerShell, and direct HTTP requests.

Following a successful download, the archive is extracted using the Shell.Application COM interface. Most variants invoke the CopyHere method with flags intended to suppress user prompts and allow extraction to proceed without user interaction. The extracted setup1.vbs script is then launched through wscript.exe to proceed with the next stage of the infection chain.

Also, one variant additionally attempts to remove Zone.Identifier alternate data streams from extracted files prior to execution, likely to reduce security warnings associated with files downloaded from the Internet.

Stage 3: Installation of remote monitoring and management software

Besides the setup1.vbs script, the ZIP archive downloaded during Stage 2 contains a preconfigured ManageEngine Endpoint Central deployment package. Inside the archive are the files required to install and register the Endpoint Central agent, including the MSI installer, configuration files, certificates, and installation scripts.

The table below summarizes the purpose of each file contained within the deployment package:

File	Description
DCAgentServerInfo.json	Endpoint Central server configuration containing management server IP addresses and ports
DMRootCA.crt	Trusted root certificate
DMRootCA-Server.crt	Server authentication certificate
README.html	Endpoint Central agent setup instructions
setup.bat	Legitimate Endpoint Central installer wrapper included in the package, not used by the malware chain
setup1.vbs	Malicious launcher used by the threat actor to silently install the Endpoint Central agent
UEMSAgent.msi	Endpoint Central agent installer package
UEMSAgent.mst	Custom installation configuration settings for the MSI package

ManageEngine Endpoint Central is a legitimate enterprise management platform commonly used for software deployment, system administration, and remote support. Its remote administration capabilities make it attractive for abuse by threat actors seeking persistent access to compromised systems.

One interesting variant attempted to disguise the package as an income tax–related document. Instead of containing a legitimate tax document, the archive contained a VBScript file named “Income Tax Return Form.vbs” and accompanied by an instruction file designed to persuade the victim to open it. Analysis showed that the VBScript contained functionality similar to setup1.vbs, ultimately performing the same Endpoint Central installation process.

As discussed in Stage 2, the downloader ultimately executes a VBScript file named setup1.vbs. The script first verifies that the required installation files are present in the extracted folder and then attempts to relaunch itself with administrative privileges using the Windows runas mechanism before proceeding with the installation.

Once elevated, setup1.vbs silently installs the bundled ManageEngine Endpoint Central agent using msiexec.exe, applying the supplied configuration and certificate files. The installation is performed silently, preventing the user from seeing the Endpoint Central installation interface.

Analysis of the embedded DCAgentServerInfo.json configuration file revealed the following Endpoint Central management servers:

• 202.61.160[.]208
• 202.61.160[.]202
• 202.61.160[.]201
• 202.61.160[.]160
• 202.61.160[.]137
• 38.55.151[.]63

Notably, 202.61.160[.]201 had previously been observed as command-and-control infrastructure associated with ValleyRAT and Gh0st RAT activity. Although the overlap raises the possibility of the VBS campaign being linked to the operator of these known malware families, the available evidence is insufficient to confidently attribute the campaign to a known threat actor.

Victimology and attribution

Based on our telemetry, infections were observed across several countries and territories, including Malaysia, Brazil, India, Mexico, Singapore, UK, Spain, Taiwan, Australia, Russia, and Vietnam, with 80% of the victims located in Malaysia. The campaign primarily relied on malicious VBScript attachments distributed through WhatsApp and appeared to target individual users rather than specific organizations or industries. At the time of the analysis, no evidence suggested a focused targeting strategy, instead indicating a broad, opportunistic campaign aimed at consumers.

We were unable to confidently attribute this activity to a known threat actor or intrusion set. However, several artifacts observed throughout the campaign point to a possible Chinese-speaking threat actor.

Multiple VBScript samples contained comments, module descriptions, and execution notes written in simplified Chinese characters. These comments appeared consistently across different variants, suggesting that the scripts were likely developed or maintained by a Chinese-speaking operator.

We also identified infrastructure overlaps with IP addresses previously associated with ValleyRAT and Gh0st RAT activity. While these overlaps may indicate infrastructure reuse or shared hosting resources, they are not sufficient to establish a direct connection to any known threat actor.

Based on the available evidence, we assess with low confidence that the campaign was conducted by a Chinese-speaking operator. Additional investigation, infrastructure overlaps, or operational indicators would be required to support a stronger attribution assessment.

Conclusion

This campaign uses compromised WhatsApp accounts to distribute malicious VBScript attachments that ultimately install a preconfigured ManageEngine Endpoint Central agent on victim systems. Observed victims were located across multiple countries and territories, including Malaysia, Brazil, India, Mexico, Singapore, UK, Spain, Taiwan, Australia, Russia, and Vietnam, suggesting a broad and opportunistic campaign. Users should be cautious when receiving unexpected attachments through WhatsApp, even when they appear to originate from known contacts. Script and executable file types such as VBS, VBE, EXE, BAT, CMD, JS, and PS1 should not be opened unless their legitimacy has been independently verified.

IOCs

VBScript

c7f38cbb99c8b74fa0465293feeba700 Financial Reports.vbs
b7cd06c71465038b658a6dc1f273a507 Debt confirmation.vbs
9f13c7b8ba391b2f597874e54d310648 Electronic statement(A).vbs
993f4c0cadbc769a4b0ed62a918db58d Financial Reports(s).vbs
7f81c1bc8cfd588e8998968e2621456e Outstanding Payment List.vbs
7403cbcc5a9c32384d431856dc48fcc9 Statement of debt (4).vbs
68c16c46f8afb9e00bbaba0207fb0a46 Debt Note (2).vbs
66442f2457eca8f47385b1fb2c6fcab8 Statement of Debt(30K).vbs
6359e6236471cbe434d0ef4c42b7f879 Applicationform1.vbs
5b6bbcc06cf08cc99e1afeda486d42fb Extrato de Conciliação.vbs
5002eca748205d544618e3bd2dedc223 Statement of Debt(29K).vbs
4f0593e8e0e8fac49429e9b45ebf7fa1 Outstanding Payment List.vbs
4044e4b6471c9de7b0a4ba37d9d9df9a billing statement (2).vbs
20209b3a32769afc6a75694b8d8839dd Statement of Debt(A).vbs
0ba93109757776a44de9d8c88baa4963 Financial Reports(C1).vbs
02bb20455cc592a69c080abac770ce90 Le formulaire de demande le plus récent .vbs
6c39900d77dcba158e1d27c7619cb06d Outstanding Balance Sheet(A).vbs
dad708e050632a4280cabf98ac1376b7 Outstanding Balance Sheet.vbs
05d188f071d097f5b6bd8138749b4b14 Penyata bank.vbs
2c6f05f1f309d89b2236e6c8b59c88f9 Account Statement（13K） (2).vbs
3b1aba44dd3d9b6339b6f56e2f42034b Statement of Account.txt
d43fdaa1f0ee09d7e5f0f94ee9df7b6c Bitte füllen Sie das Formular für Umsatzsteuer-Nullsatz-Verkäufe aus.vbs
df4fa0369eaca5cec348be293890d4af Account Statement.vbs
63ac85195b73753333316a889cf5880f Statement of Account(O).vbs
74fd9f91fc93b6288b4fc253ea5b3e20 Sila semak bil anda.vbs
d06333c360b51456f427e616c3c5f8bd Sila semak bil anda.vbs
993f4c0cadbc769a4b0ed62a918db58d FinancialReportsS.vbs
1d94fbe9cab21278cc3f104bea334d08 Promissory_Note(b).vbs
9d9ac85765e4a818a3ccabe2cf4fef82 Debt Statement.vbs
6fb6a55424adfb61e31f06aef33273e5 dfjieya.vbs
f90ed4b2d0b67114aa89ddfed658e5c0 dfjieya.vbs
8c3322009b8982663c0cbecd9492e7eb 0lf.vbs
66705384a7ad81d14c34fc6c054a0ecf iowepv.vbs
8c6d9fc389ad3f20ccbc71d77eb39bfa btksfmsi.vbs
1a3cc75466ffb1971482f7abf7aabc3f home3.vbs
1c47c63e5ed25060d95359c57c77b107 zipats.vbs
31037a42ca048e06e69a78f55bc2eff5 1122.vbs
7f16449cd0c4862d1eadf8a5742bf09a payload_1.vbs
79ecd61b09b0f2d54b34586c916c4ec9 sac8.vbs
7849061c536a3efb05a56d504694e7e7 6oy.vbs
ddaffe9849f7f3c79f8804adb9a6b3d5 kof.vbs
d01cad98dd0d01b75e04e784953c5e2b sleestak_payload_1.vbs

Domains

temu.baskwms[.]top
invoice.msopsa[.]top
qse.shoppes[.]help
shaaslong[.]one
baoxis[.]cc
baolongwes.oss-ap-southeast-1.aliyuncs[.]com
sdcwww.oss-ap-southeast-1.aliyuncs[.]com
baoyuw2s.s3.ap-southeast-1.amazonaws[.]com
hksha3.s3.ap-southeast-1.amazonaws[.]com
sjdkjj23.s3.ap-southeast-1.amazonaws[.]com
xijkwm2.s3.ap-southeast-1.amazonaws[.]com
yifubafu.s3.ap-southeast-1.amazonaws[.]com
caiwuascw.s3.us-east-005.backblazeb2[.]com
facaia.s3.us-east-005.backblazeb2[.]com

Attacker-controlled UEMS server IP Address

202.61.160[.]202
202.61.160[.]201
202.61.160[.]137
202.61.160[.]160
202.61.160[.]208
38.55.151[.]63