CVE-2023-24056: Pkgconf DOS Vulnerability

CVE-2023-24056 Overview

CVE-2023-24056 is a resource exhaustion vulnerability in pkgconf through version 1.9.3 that allows attackers to cause unbounded string expansion through maliciously crafted .pc files. The vulnerability exists in libpkgconf/tuple.c:pkgconf_tuple_parse where incorrect checks fail to prevent recursive variable duplication, enabling a small input file of only a few hundred bytes to expand to one billion bytes of memory consumption.

Critical Impact

A maliciously crafted .pc package configuration file can trigger exponential memory consumption, leading to denial of service conditions on systems processing untrusted pkgconf files.

Affected Products

• pkgconf versions through 1.9.3
• Systems using libpkgconf for package configuration parsing
• Build environments processing untrusted .pc files

Discovery Timeline

• 2023-01-22 - CVE-2023-24056 published to NVD
• 2025-04-02 - Last updated in NVD database

Technical Details for CVE-2023-24056

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write) and represents a resource exhaustion attack vector through improper handling of variable expansion in pkgconf's tuple parsing logic. The core issue stems from insufficient validation when processing recursive variable references within .pc (package configuration) files.

When pkgconf encounters variable definitions in .pc files, it performs string substitution to resolve variable references. The pkgconf_tuple_parse function in libpkgconf/tuple.c fails to properly limit the depth and breadth of variable expansion. An attacker can craft a .pc file with self-referencing or mutually-referencing variables that cause exponential growth during parsing.

The attack requires local access and user interaction—a user must process the malicious .pc file—but the impact is a complete denial of service through memory exhaustion. A carefully constructed input of merely a few hundred bytes can expand to approximately one billion bytes, overwhelming system memory.

Root Cause

The root cause lies in incorrect boundary checks within the pkgconf_tuple_parse function. The function performs variable substitution without adequately tracking or limiting the expansion depth. When variables reference each other in a pattern that causes duplication, the parser enters an expansion loop that grows exponentially rather than linearly. This oversight allows trivially small malicious input to consume massive system resources.

Attack Vector

The attack requires an adversary to deliver a malicious .pc file to a target system where it will be processed by pkgconf. This could occur through:

1. Compromised package repositories containing malicious .pc files
2. Supply chain attacks where build dependencies include crafted configuration files
3. Development environments processing third-party package configurations
4. CI/CD pipelines that build software from untrusted sources

The vulnerability enables a denial of service attack where the targeted build process or system becomes unresponsive due to memory exhaustion. While no code execution is possible through this vulnerability, the availability impact can disrupt software development and deployment pipelines.

The vulnerability mechanism involves variable duplication in .pc files where recursive references cause exponential string expansion. When the parser encounters these specially crafted variable definitions, insufficient validation allows the expansion to proceed without bounds, ultimately consuming available system memory. Technical details can be found in the Null Program blog post that analyzes this vulnerability class.

Detection Methods for CVE-2023-24056

Indicators of Compromise

• Unusual memory consumption during build processes involving pkgconf
• Build failures or system unresponsiveness when processing .pc files
• Presence of .pc files with unusually complex or deeply nested variable definitions
• Anomalous file sizes or memory allocations in build logs

Detection Strategies

• Monitor memory usage patterns during software compilation and build processes
• Implement file integrity monitoring for .pc configuration files in package repositories
• Deploy static analysis tools to scan .pc files for suspicious variable patterns before processing
• Configure resource limits (ulimit) for processes that execute pkgconf operations

Monitoring Recommendations

• Set up alerts for abnormal memory consumption in build environments
• Log and audit all .pc file processing operations in CI/CD pipelines
• Monitor for pkgconf processes that exceed normal execution time thresholds
• Track package configuration changes in software repositories

How to Mitigate CVE-2023-24056

Immediate Actions Required

• Upgrade pkgconf to version 1.9.4 or later which contains the security fix
• Review and validate all .pc files from untrusted sources before processing
• Implement memory limits for build processes using cgroups or ulimit
• Audit existing package configurations in build environments for suspicious patterns

Patch Information

The vulnerability has been addressed in the official pkgconf repository. The fix is available in commit 628b2b2bafa5d3a2017193ddf375093e70666059 which adds proper validation checks to prevent unbounded variable expansion. Users should upgrade to pkgconf version 1.9.4 or later, which includes this fix. Release versions can be verified at the pkgconf GitHub repository.

Workarounds

• Apply memory limits to processes that parse .pc files using operating system controls
• Validate and sanitize .pc files from external sources before inclusion in build processes
• Use containerized build environments with strict resource constraints to limit blast radius
• Consider temporarily disabling variable expansion in pkgconf if application requirements permit

# Configuration example: Apply memory limits to build processes
# Set memory limit to 2GB for pkgconf operations
ulimit -v 2097152

# Alternative: Use cgroups for process isolation
cgcreate -g memory:pkgconf_limit
echo 2147483648 > /sys/fs/cgroup/memory/pkgconf_limit/memory.limit_in_bytes
cgexec -g memory:pkgconf_limit pkgconf --cflags package