A sophisticated Windows remote-access trojan known as ValleyRAT has emerged as a high-confidence indicator of targeted intrusions against Chinese-language users and organizations.
ValleyRAT’s operational model relies on a carefully orchestrated delivery chain comprising four distinct components: the downloader, loader, injector, and RAT payload.
First observed in early 2023, this multi-stage malware combines advanced evasion techniques, aggressive privilege escalation, and targeted execution logic to establish persistent footholds on victim systems while evading security defenses.
This modular architecture enables operators to maintain stealth throughout the attack chain through in-memory decryption and living-off-the-land execution techniques.
The malware leverages legitimate Windows binaries, particularly MSBuild.exe, as execution hosts to disguise its presence as trusted system processes.
ValleyRAT demonstrates an unusual level of targeting sophistication through its implementation of a geographical kill switch mechanism.
Upon execution, the malware queries the Windows Registry for the presence of two popular Chinese communication applications: WeChat and DingTalk.
If both registry entries (HKCUSoftwareDingTalk and HKCUSoftwareTencentWeChat) are not found, the malware assumes it’s running outside its intended operational environment and immediately terminates execution while displaying a misleading error message.
This targeted approach distinguishes ValleyRAT from commodity malware variants and indicates operators conducting highly focused campaigns rather than opportunistic attacks.
The malware also implements an anti-duplicate-instance check by attempting to create a named mutex labeled “TEST,” preventing multiple instances from running simultaneously on compromised systems.
Security researchers treating ValleyRAT detections as high-confidence indicators of targeted intrusions rather than casual infections have identified this kill switch as a key indicator of deliberate operational security measures employed by sophisticated threat actors.
Multi-Vector Privilege Escalation
Once ValleyRAT’s environmental checks pass, the malware immediately pursues administrative access through multiple user account control (UAC) bypass techniques.
The malware exploits known Windows executables, including CompMgmtLauncher.exe, Event Viewer, and Fodhelper.exe, by manipulating both file and registry entries in user-writeable locations.
The most notable technique involves associating the ms-settings ProgID with custom file extensions in HKCUSoftwareClasses, redirecting execution flow when legitimate Windows tools are launched.
ValleyRAT additionally manipulates its security token to enable SeDebugPrivilege, granting the malware unprecedented control to interact with, inspect, and terminate processes belonging to other users or higher integrity levels.
After securing elevated privileges, ValleyRAT systematically dismantles security defenses by targeting an exhaustive list of anti-virus and host-based intrusion prevention system executables, predominantly from Chinese vendors including Qihoo 360, Tencent QQ PC Manager, and Kingsoft.
| Vendor | Targeted Executables (Examples) |
|---|---|
| Qihoo 360 | 360d.exe, 360Safe.exe, 360Tray.exe |
| Tencent QQ | QQPCRTP.exe, QQMPersonalCenter.exe |
| Kingsoft | kxscan.exe, kwsprt.exe, kxascore.exe |
The malware uses the CPUID instruction to verify processor vendor strings, checking for “GenuineIntel” or “AuthenticAMD” identifiers often spoofed in virtual environments like VMware or VirtualBox.
The malware terminates these processes before proceeding and modifies security software registry settings to turn off their autostart capabilities.
Sophisticated Anti-Analysis
ValleyRAT employs robust anti-analysis techniques to evade both sandbox environments and researcher investigation.
Through the Picus Threat Library, it replicates the tactics, techniques, and procedures (TTPs) observed in these campaigns.
| Threat ID | Threat Name | Attack Module |
|---|---|---|
| 29426 | ValleyRAT Malware Downloader Download Threat | Network Infiltration |
| 25204 | ValleyRAT Malware Downloader Email Threat | Email Infiltration |
| 59821 | ValleyRAT Loader Download Threat | Network Infiltration |
| 54856 | ValleyRAT Loader Email Threat | Email Infiltration |
| 72873 | ValleyRAT Malware Dropper Download | Network Infiltration |
| 46588 | ValleyRAT Malware Dropper Email Threat | Email Infiltration |
Additionally, the malware enumerates running windows and checks their title strings against known analysis tools including Wireshark, Fiddler, Malwarebytes, ApateDNS, and TaskExplorer.
To ensure persistent execution across system reboots, ValleyRAT writes its execution path to HKEY_CURRENT_USERSOFTWAREMicrosoftWindowsCurrentVersionRun using a deceptive value name, GFIRestart32.exe.
The malware also copies itself into the Startup folder as Appcustom.exe, establishing multiple persistence vectors.
Before contacting its command-and-control server, ValleyRAT performs an initial Internet connectivity check against hxxp://www.baidu.com, then generates a randomized integer to construct a dynamic beacon string sent to the C2 infrastructure.
This dynamic approach aids in network-based evasion by preventing static detection signatures from identifying command-and-control communications.
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