CVE-2025-49794: libxml2 Use-After-Free Vulnerability

CVE-2025-49794 is a use-after-free vulnerability in libxml2 that occurs during XPath parsing with XML schematron elements. Attackers can exploit this to crash applications or trigger undefined behavior. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2025-49794 Overview

A use-after-free vulnerability was found in libxml2. This issue occurs when parsing XPath elements under certain circumstances when the XML schematron has the <sch:name path="..."/> schema elements. This flaw allows a malicious actor to craft a malicious XML document used as input for libxml, resulting in the program's crash using libxml or other possible undefined behaviors.

Critical Impact
This vulnerability could lead to program crashes or other undefined behaviors, posing a significant risk of denial of service and potential code execution.

Affected Products

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Discovery Timeline

2025-06-16 - CVE CVE-2025-49794 published to NVD
2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-49794

Vulnerability Analysis

The vulnerability is a use-after-free condition in the libxml2 library. It arises during the processing of crafted XML documents that include specific XPath elements that libxml2 parses incorrectly, leading to memory being freed multiple times. This improper handling can cause the program to crash and may open avenues for arbitrary code execution.

Root Cause

The root cause is an incorrect management of memory when XPath elements are parsed. Specifically, when XML schematrons with <sch:name path="..."/> elements are processed, libxml2 does not handle memory references properly.

Attack Vector

This vulnerability can be exploited remotely by providing a specially crafted XML document to the affected software using libxml2 for XML parsing.

// Example exploitation code (sanitized)
char *xml_str = "<root><sch:name path='...'/></root>";
doc = xmlParseDoc((const xmlChar *)xml_str);
processDoc(doc);
xmlFreeDoc(doc);  // Improper handling could lead to use-after-free

Detection Methods for CVE-2025-49794

Indicators of Compromise

Unusual crashes in applications using libxml2
Log entries showing parsing of suspicious XML content
Unexpected memory access errors

Detection Strategies

Utilize runtime analysis tools that monitor memory allocation and deallocation patterns to detect possible use-after-free conditions. SentinelOne's behavior-based detection can flag anomalies in application execution patterns typical of this vulnerability.

Monitoring Recommendations

Continuously monitor application logs for anomalies related to XML parsing. Implement host-based intrusion detection systems with rulesets targeting memory corruption vulnerabilities. Utilize SentinelOne's threat intelligence for real-time anomaly detection.

How to Mitigate CVE-2025-49794

Immediate Actions Required

Disable processing of XML schematrons with XPath elements where possible
Restrict network access to vulnerable applications
Implement application whitelisting to prevent execution of untrusted code

Patch Information

Ensure all deployments of libxml2 are updated to the latest patched version provided by the respective vendor to mitigate this vulnerability. Refer to RedHat Advisories for detailed patch information.

Workarounds

Consider using application firewall rules to strip suspicious XML elements before processing if patching is delayed.

bash

# Configuration example
iptables -A INPUT -p tcp --dport 80 -m string --string "<sch:name" --algo bm --to 65535 -j DROP