CVE-2025-5745: GNU Glibc Privilege Escalation Vulnerability

CVE-2025-5745 Overview

A vulnerability has been discovered in the GNU C Library (glibc) affecting the strncmp implementation optimized for Power10 processors. The flaw involves improper initialization where the function writes to vector registers v20 to v31 without preserving the caller's contents. According to the powerpc64le ABI, these registers are defined as non-volatile and their contents should be preserved across function calls.

This improper handling can result in overwriting register contents, potentially altering the control flow of the calling application or leaking input strings to other parts of the program.

Critical Impact

Applications running on Power10 processors using glibc 2.40+ may experience unexpected behavior, memory corruption, or information leakage when invoking strncmp operations.

Affected Products

• GNU glibc version 2.40 and later
• Systems running on Power10 (POWER10) processors with powerpc64le architecture
• Applications utilizing the optimized strncmp implementation

Discovery Timeline

• June 5, 2025 - CVE-2025-5745 published to NVD
• October 22, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5745

Vulnerability Analysis

This vulnerability stems from improper initialization of resources (CWE-665) in the Power10-optimized strncmp assembly implementation within glibc. The powerpc64le Application Binary Interface (ABI) designates vector registers v20 through v31 as non-volatile, meaning any function that uses these registers must first save their contents and restore them before returning to the caller.

The optimized strncmp implementation violates this ABI contract by directly writing to these non-volatile vector registers without the required save and restore operations. This can have two significant consequences: first, the caller's data stored in these registers gets corrupted, potentially causing incorrect program behavior or crashes; second, the input strings passed to strncmp may persist in these registers and become accessible to unrelated code paths, creating an information disclosure risk.

Root Cause

The root cause is an ABI compliance failure in the Power10-optimized assembly code for strncmp. The function implementation uses vector registers v20-v31 for performance optimization but fails to implement the required register preservation protocol mandated by the powerpc64le ABI. This is a classic example of improper initialization (CWE-665) where resources are not properly managed according to their defined contracts.

Attack Vector

Exploitation requires an attacker to influence strncmp operations on a vulnerable system running on Power10 architecture. The network attack vector with high complexity indicates that while remote triggering is possible through applications that process network-supplied strings using strncmp, successful exploitation depends on specific conditions including the application's use of non-volatile registers after the strncmp call.

Attack scenarios include:

• Triggering strncmp comparisons with crafted strings to corrupt specific register values
• Exploiting register corruption to alter program control flow in security-sensitive operations
• Leveraging register leakage to extract sensitive data from previous strncmp comparisons

For detailed technical information about this vulnerability, see the Sourceware Bug Report #33060.

Detection Methods for CVE-2025-5745

Indicators of Compromise

• Unexpected application crashes or segmentation faults on Power10 systems after string comparison operations
• Anomalous program behavior in applications performing intensive strncmp operations
• Debug logs showing register corruption or unexpected values in vector registers v20-v31

Detection Strategies

• Monitor system logs for crashes related to string comparison functions in glibc on Power10 systems
• Deploy runtime monitoring for applications that heavily utilize strncmp operations
• Implement application-level integrity checks to detect unexpected control flow changes

Monitoring Recommendations

• Track glibc version deployment across Power10 infrastructure to identify systems running version 2.40 or later
• Enable crash dump analysis on critical systems to identify patterns consistent with register corruption
• Monitor for unusual information disclosure patterns in applications processing sensitive string data

How to Mitigate CVE-2025-5745

Immediate Actions Required

• Identify all Power10 systems running glibc version 2.40 or later
• Evaluate the criticality of applications performing string comparison operations on affected systems
• Consider downgrading to a glibc version prior to 2.40 where the Power10 optimization is not present
• Monitor the Sourceware Bug Report #33060 for patch availability

Patch Information

No official patch has been confirmed at the time of this analysis. Organizations should monitor GNU glibc security announcements and the Sourceware bug tracker for updates. When a patch becomes available, prioritize deployment on Power10 systems running affected glibc versions.

Workarounds

• Disable Power10-specific optimizations in glibc by recompiling with generic implementations
• Use alternative string comparison functions that do not rely on the vulnerable optimized code path
• Isolate critical applications from potential register corruption by implementing additional validation layers
• Consider containerization or process isolation to limit the impact of potential register leakage

# Check glibc version on affected systems
ldd --version

# Identify Power10 architecture
cat /proc/cpuinfo | grep -i power10

# Monitor for systems with affected configuration
rpm -qa | grep glibc  # For RPM-based systems
dpkg -l | grep libc6  # For Debian-based systems