CVE-2024-34459: Xmlsoft Libxml2 Buffer Overflow Flaw

CVE-2024-34459 Overview

CVE-2024-34459 is a buffer over-read vulnerability discovered in xmllint, a command-line XML tool that is part of the libxml2 library. The vulnerability exists in the xmlHTMLPrintFileContext function within xmllint.c and can be triggered when formatting error messages using the --htmlout option. This flaw allows attackers to potentially read sensitive data from memory beyond the intended buffer boundaries, leading to information disclosure.

libxml2 is one of the most widely deployed XML parsing libraries, used extensively across Linux distributions, macOS, and numerous applications that require XML processing capabilities. The vulnerability affects versions prior to 2.11.8 and versions 2.12.x before 2.12.7.

Critical Impact

This buffer over-read vulnerability can expose sensitive information from process memory when xmllint processes malformed input with HTML output enabled, potentially leaking credentials, cryptographic keys, or other confidential data.

Affected Products

• xmlsoft libxml2 versions before 2.11.8
• xmlsoft libxml2 versions 2.12.x before 2.12.7
• Systems and applications that integrate vulnerable libxml2 versions

Discovery Timeline

• May 14, 2024 - CVE-2024-34459 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2024-34459

Vulnerability Analysis

The vulnerability is classified as CWE-122 (Heap-based Buffer Overflow), though the specific manifestation is a buffer over-read condition. When xmllint is invoked with the --htmlout flag to format error messages as HTML output, the xmlHTMLPrintFileContext function fails to properly validate buffer boundaries before reading data. This improper bounds checking allows the function to read memory beyond the allocated buffer, potentially exposing adjacent memory contents.

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker can craft malicious XML input that, when processed by xmllint with HTML output formatting, triggers the over-read condition. The primary impact is confidentiality compromise through information disclosure, as the vulnerability does not directly enable code execution or data modification.

Root Cause

The root cause lies in insufficient boundary validation within the xmlHTMLPrintFileContext function in xmllint.c. When this function formats file context information for HTML error output, it reads character data without properly verifying that the read operations remain within the allocated buffer's boundaries. This oversight allows reads to extend past the legitimate buffer extent, accessing unintended memory regions.

Attack Vector

An attacker can exploit this vulnerability by:

1. Crafting a malicious XML document designed to trigger error conditions during parsing
2. Ensuring the target system processes the document using xmllint --htmlout
3. The error formatting routine reads beyond buffer boundaries
4. Sensitive data from adjacent memory regions is included in the HTML output
5. The attacker receives the output containing the leaked information

The vulnerability requires no special privileges and can be triggered through normal XML processing operations when the vulnerable command-line options are used. Systems that expose xmllint functionality to process untrusted input are at particular risk.

Detection Methods for CVE-2024-34459

Indicators of Compromise

• Unusual or unexpected output from xmllint processes containing non-printable characters or garbage data
• Error messages with corrupted or unexpected content when using --htmlout option
• Abnormal memory access patterns detected by memory sanitizers or debugging tools
• Unexpected data leakage in application logs that use libxml2 for XML processing

Detection Strategies

• Monitor for xmllint processes invoked with the --htmlout flag processing untrusted input
• Implement application-level logging to track XML parsing errors and unusual output patterns
• Deploy memory safety tools (AddressSanitizer, Valgrind) in development and staging environments to detect over-read conditions
• Use SentinelOne's behavioral analysis to detect anomalous memory access patterns in processes using libxml2

Monitoring Recommendations

• Audit systems for installed libxml2 versions and flag vulnerable versions for remediation
• Monitor network traffic for potential exploitation attempts targeting XML processing endpoints
• Implement file integrity monitoring on libxml2 library files to detect unauthorized modifications
• Track xmllint process execution with command-line argument logging to identify risky invocations

How to Mitigate CVE-2024-34459

Immediate Actions Required

• Update libxml2 to version 2.11.8 or later (for 2.11.x branch) or 2.12.7 or later (for 2.12.x branch)
• Apply vendor-provided patches from Fedora, Debian, or other distribution security advisories
• Audit applications and scripts that invoke xmllint with the --htmlout option and assess exposure
• Restrict processing of untrusted XML input through xmllint until patches are applied

Patch Information

The vulnerability has been addressed in libxml2 releases v2.11.8 and v2.12.7. The fix corrects the boundary checking logic in the xmlHTMLPrintFileContext function to prevent out-of-bounds memory reads. Detailed patch information is available through the GNOME libxml2 Release v2.11.8 and GNOME libxml2 Release v2.12.7. The original issue is tracked at GNOME libxml2 Issue #720.

Distribution-specific patches are available via Fedora Package Announcements and Debian LTS Announcement.

Workarounds

• Avoid using the --htmlout option with xmllint when processing untrusted XML input
• Implement input validation and sanitization before passing XML documents to xmllint
• Use alternative XML validation tools that are not affected by this vulnerability until patching is complete
• Deploy application sandboxing to limit the potential impact of information disclosure

# Check installed libxml2 version
xmllint --version

# Verify if vulnerable version is installed
# Vulnerable: versions before 2.11.8 or 2.12.x before 2.12.7
# Update via package manager (example for apt-based systems)
sudo apt update && sudo apt install --only-upgrade libxml2 libxml2-utils

# For RPM-based systems
sudo dnf update libxml2