CVE-2025-5702: GNU Glibc Privilege Escalation Vulnerability

CVE-2025-5702 Overview

A vulnerability exists in the GNU C Library (glibc) version 2.39 and later affecting systems with Power10 processors. The strcmp implementation optimized for Power10 architecture improperly initializes vector registers, writing to registers v20 through v31 without preserving the caller's data. These registers are designated as non-volatile by the powerpc64le ABI specification, meaning the callee is responsible for saving and restoring their contents. This improper initialization can result in data corruption, altered control flow, or information leakage.

Critical Impact

The vulnerability can overwrite non-volatile register contents, potentially altering program control flow or leaking sensitive string data to other parts of the application.

Affected Products

• GNU glibc version 2.39 and later
• Systems running powerpc64le architecture with Power10 processors
• Applications using the optimized strcmp function on affected platforms

Discovery Timeline

• 2025-06-05 - CVE CVE-2025-5702 published to NVD
• 2025-10-01 - Last updated in NVD database

Technical Details for CVE-2025-5702

Vulnerability Analysis

This vulnerability stems from improper initialization of processor registers in architecture-specific optimized code. The Power10-optimized strcmp implementation in glibc violates the powerpc64le Application Binary Interface (ABI) conventions by writing to vector registers v20-v31 without first saving their contents. According to the ABI specification, these registers are classified as non-volatile, meaning any function that modifies them must preserve and restore their original values.

The improper handling creates two distinct security concerns. First, the caller's register contents are overwritten without preservation, potentially corrupting program state and altering execution flow. Second, the input strings passed to strcmp may persist in these registers after the function returns, creating an information disclosure pathway where sensitive data could be exposed to other parts of the program.

This vulnerability is classified under CWE-665 (Improper Initialization), as the function fails to properly initialize and preserve the state of non-volatile resources it utilizes.

Root Cause

The root cause is a violation of the powerpc64le ABI calling conventions in the Power10-optimized strcmp assembly implementation. The optimized code utilizes vector registers v20-v31 for performance gains but neglects to implement the required save/restore prologue and epilogue that would preserve the caller's register state. This ABI violation means any calling function that stores values in these non-volatile registers expects them to remain unchanged after the strcmp call returns, but the optimized implementation corrupts these values.

Attack Vector

The vulnerability can be exploited through network-accessible interfaces where attacker-controlled strings are compared using strcmp. An attacker could potentially craft specific input strings that, when processed by the vulnerable strcmp implementation, corrupt register state in a way that alters program control flow or causes sensitive data leakage. The network attack vector requires high complexity to exploit successfully, as the attacker must understand the target application's register usage patterns and timing.

The vulnerability mechanism involves:

1. A calling function stores important data in non-volatile registers v20-v31
2. The function calls strcmp with attacker-influenced input
3. The Power10-optimized strcmp overwrites these registers without preservation
4. The calling function resumes execution with corrupted register state
5. Program behavior becomes undefined, potentially leading to security violations

For detailed technical analysis of the register handling issue, see the Sourceware Bug Report #33056.

Detection Methods for CVE-2025-5702

Indicators of Compromise

• Unexpected application crashes or segmentation faults on Power10 systems after glibc 2.39 upgrade
• Anomalous program behavior when processing string comparison operations
• Memory corruption indicators in applications heavily utilizing strcmp operations
• Unexplained data exposure or leakage in multi-threaded applications

Detection Strategies

• Monitor for unexpected application terminations with register-related crash signatures on Power10 systems
• Audit glibc versions deployed on powerpc64le architecture systems to identify version 2.39 and later installations
• Implement runtime integrity checking for applications that depend heavily on string comparison functions
• Review application logs for signs of control flow anomalies or unexpected behavior patterns

Monitoring Recommendations

• Enable detailed crash reporting and core dump analysis on affected Power10 systems
• Implement application performance monitoring to detect subtle behavioral changes
• Configure security information and event management (SIEM) rules to correlate unusual application behavior with Power10 system usage
• Establish baseline behavior metrics for critical applications to identify deviations

How to Mitigate CVE-2025-5702

Immediate Actions Required

• Identify all systems running powerpc64le architecture with Power10 processors
• Audit glibc versions to determine exposure to versions 2.39 and later
• Prioritize patching for systems processing sensitive data or exposed to untrusted input
• Consider temporarily disabling Power10-specific optimizations if available through environment variables

Patch Information

A fix for this vulnerability has been tracked in the GNU C Library bug tracker. System administrators should monitor the Sourceware Bug Report #33056 for patch availability and apply the corrected glibc version when released by their distribution vendor. The fix involves proper implementation of register save/restore operations in the Power10 strcmp assembly code to comply with the powerpc64le ABI specification.

Workarounds

• Compile applications with optimization flags that avoid the Power10-specific strcmp implementation if possible
• Use alternative string comparison functions that do not utilize the vulnerable optimized code path
• Implement application-level input validation to reduce exposure to attacker-controlled string comparisons
• Consider using glibc version 2.38 or earlier on affected Power10 systems until patches are available

# Check glibc version on affected systems
ldd --version

# Identify Power10 processor
grep -i power /proc/cpuinfo

# Example: Set environment variable to potentially disable optimized routines (if supported)
export GLIBC_TUNABLES=glibc.cpu.hwcaps=-ARCH_3_1