CVE-2022-22824: Libexpat Integer Overflow Vulnerability

CVE-2022-22824 Overview

CVE-2022-22824 is an integer overflow vulnerability in the defineAttribute function within xmlparse.c of the Expat (libexpat) XML parsing library prior to version 2.4.3. This vulnerability allows remote attackers to exploit the integer overflow condition through specially crafted XML input, potentially leading to remote code execution, denial of service, or other security impacts.

Critical Impact

This integer overflow vulnerability in a widely-used XML parsing library can be exploited remotely without authentication, potentially enabling attackers to execute arbitrary code or crash applications that rely on libexpat for XML processing.

Affected Products

• libexpat_project libexpat (versions before 2.4.3)
• tenable nessus
• debian debian_linux (versions 10.0 and 11.0)
• siemens sinema_remote_connect_server

Discovery Timeline

• 2022-01-10 - CVE-2022-22824 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2022-22824

Vulnerability Analysis

The vulnerability exists in the defineAttribute function of xmlparse.c, which is responsible for handling XML attribute definitions during parsing. When processing certain XML inputs, an integer overflow condition can occur due to insufficient bounds checking on numeric calculations within the attribute handling logic. This integer overflow (CWE-190) can lead to incorrect memory allocations, buffer overflows, or other memory corruption conditions.

The network-based attack vector means the vulnerability can be exploited remotely when an application parses untrusted XML data received over a network connection. No privileges or user interaction are required to exploit this vulnerability, making it particularly dangerous for any service that processes external XML content.

Root Cause

The root cause is an integer overflow condition in the defineAttribute function. When computing buffer sizes or index values related to XML attribute processing, the code performs arithmetic operations that can overflow when dealing with maliciously large or specially crafted values. This results in unexpected behavior when the overflowed value is subsequently used for memory operations.

Attack Vector

An attacker can exploit this vulnerability by sending maliciously crafted XML content to an application that uses a vulnerable version of libexpat for parsing. The attack scenario involves:

1. The attacker crafts an XML document with attributes designed to trigger the integer overflow in defineAttribute
2. The target application receives and attempts to parse the malicious XML
3. The integer overflow causes memory corruption or unexpected code execution
4. Depending on the application context, this could result in remote code execution, information disclosure, or denial of service

The vulnerability is exploited over the network and requires no authentication or user interaction, making automated exploitation feasible against exposed services.

Detection Methods for CVE-2022-22824

Indicators of Compromise

• Unusual XML parsing errors or crashes in applications using libexpat
• Abnormally large or malformed XML documents in application logs
• Unexpected memory consumption spikes during XML processing operations
• Application crashes with memory corruption indicators in core dumps

Detection Strategies

• Implement intrusion detection rules to identify anomalous XML payloads with oversized attribute values
• Monitor application logs for XML parsing exceptions or segmentation faults
• Use software composition analysis (SCA) tools to identify vulnerable libexpat versions in your environment
• Deploy endpoint detection and response (EDR) solutions to detect exploitation attempts

Monitoring Recommendations

• Enable verbose logging for XML parsing operations in critical applications
• Monitor network traffic for unusually large XML payloads targeting XML-processing services
• Implement file integrity monitoring on libexpat library files
• Configure alerts for application crashes that may indicate exploitation attempts

How to Mitigate CVE-2022-22824

Immediate Actions Required

• Update libexpat to version 2.4.3 or later immediately
• Identify all applications in your environment that depend on libexpat
• Prioritize patching for internet-facing services that process external XML data
• Consider implementing input validation and size limits for XML documents as a defense-in-depth measure

Patch Information

The vulnerability has been addressed in libexpat version 2.4.3. The fix is available through the GitHub Pull Request for Expat. Multiple downstream vendors have released their own security advisories:

• Debian DSA-5073 Advisory - Security update for Debian Linux
• Tenable Security Notice TNS-2022-05 - Nessus security update
• Siemens Security Certificate SSA-484086 - SINEMA Remote Connect Server update
• Gentoo GLSA 202209-24 - Gentoo Linux security advisory

Workarounds

• Restrict XML parsing to trusted sources only where possible
• Implement strict input validation and size limits on XML documents before parsing
• Deploy web application firewalls (WAF) with rules to filter malicious XML payloads
• Consider using sandboxed or isolated environments for processing untrusted XML content

# Check libexpat version on Linux systems
dpkg -l | grep libexpat
rpm -qa | grep expat

# Update libexpat on Debian/Ubuntu
sudo apt-get update && sudo apt-get upgrade libexpat1

# Update libexpat on RHEL/CentOS
sudo yum update expat