CVE-2025-15281: GNU C Library (glibc) DoS Vulnerability

CVE-2025-15281 Overview

CVE-2025-15281 is an uninitialized memory use vulnerability in the GNU C Library (glibc) affecting versions 2.0 through 2.42. The vulnerability occurs when the wordexp() function is called with both WRDE_REUSE and WRDE_APPEND flags simultaneously. This improper flag combination causes the interface to return uninitialized memory in the we_wordv member of the wordexp_t structure. Subsequent calls to wordfree() may then attempt to free this uninitialized memory, resulting in process termination.

Critical Impact

Applications using the vulnerable wordexp() function with specific flag combinations can be crashed remotely, leading to denial of service conditions affecting system availability.

Affected Products

• GNU C Library (glibc) version 2.0 through version 2.42
• Linux distributions and systems using affected glibc versions
• Applications utilizing the wordexp() function with WRDE_REUSE and WRDE_APPEND flags

Discovery Timeline

• 2026-01-20 - CVE-2025-15281 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2025-15281

Vulnerability Analysis

This vulnerability is classified as CWE-908 (Use of Uninitialized Resource). The wordexp() function in glibc is designed to perform word expansion similar to a POSIX shell, expanding wildcards, tilde notation, and environment variables in a string. The function accepts flags that modify its behavior, including WRDE_REUSE (which indicates that a wordexp_t structure is being reused) and WRDE_APPEND (which appends expansion results to existing words).

When these two flags are combined, a logic error in the memory management code causes the we_wordv member to contain pointers to uninitialized memory locations. This occurs because the reuse logic conflicts with the append behavior, leaving memory in an indeterminate state. When wordfree() is subsequently called to release the resources, it attempts to dereference and free these uninitialized pointers, triggering undefined behavior that typically manifests as a process abort.

The network attack vector allows remote exploitation in scenarios where an attacker can influence input strings passed to applications that utilize wordexp() for shell-like expansion processing.

Root Cause

The root cause lies in improper initialization handling within the wordexp() implementation when processing the combination of WRDE_REUSE and WRDE_APPEND flags. The function fails to properly initialize or validate the we_wordv array when reusing a structure while simultaneously attempting to append results. This results in the structure containing pointers that reference arbitrary memory locations rather than properly allocated strings.

Attack Vector

An attacker can exploit this vulnerability by triggering the vulnerable code path in any application that:

1. Accepts external input for word expansion operations
2. Uses wordexp() with both WRDE_REUSE and WRDE_APPEND flags
3. Calls wordfree() on the resulting structure

The vulnerability can be exploited remotely over the network without requiring authentication or user interaction. The exploitation results in process termination, causing denial of service. While the vulnerability does not directly allow code execution or data exfiltration, the availability impact is significant for applications relying on continuous operation.

The vulnerability mechanism involves passing specially crafted input to trigger the wordexp() function call with the problematic flag combination. When the application subsequently calls wordfree() to clean up resources, the uninitialized memory access causes an abort. For technical details, see the Sourceware Bug Report #33814.

Detection Methods for CVE-2025-15281

Indicators of Compromise

• Unexpected application crashes with abort signals (SIGABRT) in processes using glibc word expansion functions
• Core dumps indicating memory corruption or invalid free operations in wordfree()
• Application logs showing abnormal termination during input processing operations
• Increased frequency of process restarts for services utilizing wordexp() functionality

Detection Strategies

• Monitor system logs for SIGABRT signals and process terminations related to memory management errors
• Implement application-level logging around wordexp() and wordfree() function calls to detect anomalous behavior
• Use memory debugging tools such as Valgrind or AddressSanitizer to identify uninitialized memory access patterns
• Deploy intrusion detection rules to identify patterns of repeated application crashes that may indicate exploitation attempts

Monitoring Recommendations

• Enable core dump collection and analysis for applications known to use glibc word expansion functions
• Implement service health monitoring with automatic alerting for unexpected process terminations
• Monitor system resource utilization for patterns consistent with denial of service attacks
• Review application dependencies to identify which services may be vulnerable to this specific issue

How to Mitigate CVE-2025-15281

Immediate Actions Required

• Identify all applications and services using glibc versions 2.0 through 2.42 that may call wordexp() with the vulnerable flag combination
• Prioritize patching systems running network-accessible services that process external input through word expansion
• Consider implementing application-level input validation to restrict characters that trigger word expansion
• Review code for usage of WRDE_REUSE in combination with WRDE_APPEND and refactor if possible

Patch Information

Update glibc to a patched version that addresses the uninitialized memory issue in wordexp(). Consult your Linux distribution's security advisories for specific package updates. For detailed information about the fix, see the Sourceware Bug Report #33814 and the OpenWall OSS-Security Discussion.

Workarounds

• Avoid using WRDE_REUSE and WRDE_APPEND flags together in wordexp() calls until the system is patched
• Refactor application code to use separate wordexp_t structures for each expansion operation rather than reusing structures
• Implement wrapper functions that validate flag combinations before calling wordexp() to prevent the vulnerable configuration
• Consider using alternative methods for shell-like expansion such as glob() for simple wildcard expansion where applicable

# Check installed glibc version
ldd --version

# Identify processes using wordexp (requires debugging symbols)
grep -r "wordexp" /usr/share/man/

# Update glibc on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade libc6

# Update glibc on RHEL/CentOS systems
sudo yum update glibc