MemProcFS DLL and Shared Library Hijacking Vulnerability

MemProcFS before version 5.17 is vulnerable to DLL and shared library hijacking due to unsafe library loading practices. Specifically, the application uses bare-name LoadLibraryU and dlopen calls without proper path qualification for vmmpyc, libMSCompression, and plugin DLLs. This vulnerability, identified as CVE-2026-40031, exists across six attack surfaces. The vulnerability was reported by VulnCheck. Exploitation can occur on both Windows and Linux systems where MemProcFS is installed.

Attack Chain

1. Attacker identifies a vulnerable MemProcFS installation (version < 5.17).
2. Attacker determines the libraries MemProcFS attempts to load without a fully qualified path, such as vmmpyc, libMSCompression, or plugin DLLs.
3. Attacker crafts a malicious DLL or shared library with the same name as one of the targeted libraries (e.g., vmmpyc.dll on Windows or libvmmpyc.so on Linux).
4. Attacker places the malicious library in the same working directory as MemProcFS or manipulates the LD_LIBRARY_PATH environment variable (on Linux) to point to a directory containing the malicious library.
5. The user executes MemProcFS.
6. MemProcFS attempts to load the legitimate library using LoadLibraryU or dlopen.
7. Due to the presence of the malicious library in the working directory or the manipulated LD_LIBRARY_PATH, the malicious library is loaded instead of the intended legitimate library.
8. The malicious library executes arbitrary code within the context of the MemProcFS process, granting the attacker control over the system.

Impact

Successful exploitation of CVE-2026-40031 allows an attacker to achieve arbitrary code execution. While the exact number of victims is unknown, any system running a vulnerable version of MemProcFS is at risk. Given the nature of MemProcFS, successful exploitation could lead to sensitive data exposure or complete system compromise.

Recommendation

• Upgrade MemProcFS to version 5.17 or later to address the vulnerability (References: https://github.com/ufrisk/MemProcFS/releases/tag/v5.17).
• Monitor process creations for MemProcFS loading unexpected DLLs or shared libraries from non-standard paths using the provided Sigma rules.
• Implement file integrity monitoring for MemProcFS installation directories to detect the presence of newly created DLLs or shared libraries with suspicious names.
• Educate users about the risks of running applications from untrusted sources and the importance of verifying the integrity of software before execution.