CVE-2025-49794: Critical Use-After-Free Vulnerability in Libxml2

Overview

The cybersecurity community is currently facing a serious vulnerability in libxml2, a widely-used software library for parsing and manipulating XML documents. The vulnerability, identified as CVE-2025-49794, is a use-after-free flaw that potentially allows malicious actors to compromise systems using a carefully crafted XML document. This vulnerability is particularly dangerous due to the widespread usage of the libxml2 library in various software applications, making a large number of systems potentially susceptible to breaches.

Vulnerability Summary

CVE ID: CVE-2025-49794
Severity: Critical (CVSS 9.1)
Attack Vector: Remote
Privileges Required: None
User Interaction: Required
Impact: System compromise and potential data leakage

Affected Products

Product | Affected Versions

Libxml2 | All versions prior to patch

How the Exploit Works

The vulnerability stems from a use-after-free issue in libxml2 when parsing XPath elements under specific circumstances. This issue occurs when the XML schematron includes the schema elements. A malicious actor can exploit this flaw by crafting a malicious XML document and feeding it as input to an application that uses the vulnerable libxml2 library. This action can result in a crash of the application, or even more concerning, lead to unexpected and potentially harmful behavior, such as a system compromise or data leakage.

Conceptual Example Code

Below is a conceptual example of an XML document that might be used to exploit this vulnerability:

<?xml version="1.0" encoding="UTF-8" ?>
<root>
<sch:name path="...">
<!-- Malicious payload here -->
</sch:name>
</root>

In this theoretical example, the malicious payload would be placed in the path field, and this document would be used as input for an application utilizing the vulnerable libxml2 library.

Mitigation Guidance

While vendors are working on patches to address this issue, it is recommend that users implement a Web Application Firewall (WAF) or Intrusion Detection System (IDS) as temporary mitigation measures. These systems can help detect and block malicious XML documents and prevent them from being processed by the vulnerable libxml2 library. Users are advised to update their libxml2 library to the patched version as soon as it becomes available to permanently rectify this vulnerability.