CVE-2026-40031: MemProcFS DLL Hijacking RCE Vulnerability

CVE-2026-40031 Overview

MemProcFS before version 5.17 contains multiple unsafe library-loading patterns that enable DLL and shared-library hijacking across six attack surfaces. The vulnerability exists due to bare-name LoadLibraryU and dlopen calls without path qualification for vmmpyc, libMSCompression, and plugin DLLs. An attacker who places a malicious DLL or shared library in the working directory or manipulates LD_LIBRARY_PATH can achieve arbitrary code execution when MemProcFS loads.

Critical Impact

Successful exploitation allows attackers to execute arbitrary code in the context of MemProcFS, potentially leading to full system compromise through DLL hijacking or shared library injection attacks.

Affected Products

• MemProcFS versions prior to 5.17
• Systems running MemProcFS with unqualified library loading patterns
• Environments where working directory or LD_LIBRARY_PATH can be manipulated

Discovery Timeline

• 2026-04-08 - CVE CVE-2026-40031 published to NVD
• 2026-04-08 - Last updated in NVD database

Technical Details for CVE-2026-40031

Vulnerability Analysis

This vulnerability falls under CWE-427 (Uncontrolled Search Path Element), a category of flaws where applications load libraries using relative paths or unqualified names. MemProcFS exhibited this weakness across six distinct attack surfaces, making it vulnerable to DLL hijacking on Windows and shared library injection on Linux/Unix systems.

The core issue stems from how MemProcFS handles library loading operations. When the application calls LoadLibraryU on Windows or dlopen on Unix-like systems without specifying absolute paths, the operating system follows its standard search order. This allows an attacker to place a malicious library in a location searched before the legitimate library path—such as the current working directory or a manipulated LD_LIBRARY_PATH.

The affected components include vmmpyc (Python bindings), libMSCompression, and various plugin DLLs. Each represents a potential entry point for code execution when MemProcFS initializes and loads its dependencies.

Root Cause

The root cause is the use of bare library names in dynamic loading functions without path qualification. Instead of specifying absolute paths to trusted library locations, the code relied on the operating system's default search behavior, which prioritizes the current working directory and environment-specified paths over system directories.

Attack Vector

An attacker can exploit this vulnerability through local access by:

1. Placing a malicious DLL or .so file with a name matching one of the targeted libraries in the application's working directory
2. Manipulating the LD_LIBRARY_PATH environment variable on Unix systems to include a directory containing the malicious library
3. Exploiting scenarios where users launch MemProcFS from untrusted locations such as Downloads folders or network shares

When MemProcFS initializes and attempts to load its dependencies, the malicious library executes attacker-controlled code with the privileges of the running process.

#define VERSION_MAJOR               5
#define VERSION_MINOR               16
-#define VERSION_REVISION            12
-#define VERSION_BUILD               226
+#define VERSION_REVISION            13
+#define VERSION_BUILD               227

#define VER_FILE_DESCRIPTION_STR    "MemProcFS : Plugin vmemd"
#define VER_FILE_VERSION            VERSION_MAJOR, VERSION_MINOR, VERSION_REVISION, VERSION_BUILD

Source: GitHub Commit Update

Detection Methods for CVE-2026-40031

Indicators of Compromise

• Unexpected DLL or shared library files appearing in MemProcFS working directories with names like vmmpyc.dll, libMSCompression.dll, or plugin-related filenames
• Process execution anomalies where MemProcFS loads libraries from non-standard locations
• Suspicious modifications to LD_LIBRARY_PATH environment variables in startup scripts or user profiles

Detection Strategies

• Monitor file creation events in directories where MemProcFS is commonly executed, looking for DLL or .so files with names matching known MemProcFS dependencies
• Implement application whitelisting to ensure only signed and verified libraries are loaded by MemProcFS
• Use endpoint detection tools to alert on library loading from unexpected paths or working directories

Monitoring Recommendations

• Enable detailed process auditing to capture library load events including source paths
• Configure SentinelOne to monitor for DLL sideloading behaviors and suspicious library loading patterns
• Regularly audit systems running MemProcFS for unauthorized library files in application directories

How to Mitigate CVE-2026-40031

Immediate Actions Required

• Upgrade MemProcFS to version 5.17 or later immediately
• Audit existing MemProcFS installations for any suspicious DLL or shared library files in working directories
• Ensure MemProcFS is launched from trusted directories with restricted write access
• Review and restrict LD_LIBRARY_PATH configurations on Unix systems

Patch Information

The vulnerability has been addressed in MemProcFS version 5.17. The fix implements proper path qualification for library loading operations, preventing the application from loading libraries from untrusted locations. For detailed patch information, refer to the GitHub Release v5.17 and the security commit. Additional technical details are available in the VulnCheck Advisory.

Workarounds

• Run MemProcFS only from directories where unprivileged users cannot write files
• On Windows, configure the SafeDllSearchMode registry key to exclude the current directory from the DLL search path
• On Unix systems, avoid setting LD_LIBRARY_PATH to include user-writable directories when running MemProcFS

# Windows: Enable SafeDllSearchMode to mitigate DLL hijacking
reg add "HKLM\System\CurrentControlSet\Control\Session Manager" /v SafeDllSearchMode /t REG_DWORD /d 1 /f

# Linux: Launch MemProcFS with a sanitized library path
LD_LIBRARY_PATH=/usr/local/lib/memprocfs ./memprocfs