CVE-2024-40896 in libxml2
Summary
by MITRE • 12/23/2024
In libxml2 2.11 before 2.11.9, 2.12 before 2.12.9, and 2.13 before 2.13.3, the SAX parser can produce events for external entities even if custom SAX handlers try to override entity content (by setting "checked"). This makes classic XXE attacks possible.
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Analysis
by VulDB Data Team • 12/22/2025
The vulnerability identified as CVE-2024-40896 affects the libxml2 library, a widely used XML parsing library in numerous applications and systems across the software ecosystem. This issue specifically impacts versions prior to 2.11.9, 2.12.9, and 2.13.3, creating a significant security risk that undermines the expected behavior of XML parsers when handling external entities. The flaw resides in the SAX (Simple API for XML) parser implementation, which is designed to provide a streaming interface for processing XML documents. The vulnerability allows attackers to bypass security controls that should prevent external entity resolution, effectively undermining the fundamental security assumptions of XML processing applications.
The technical root cause of this vulnerability stems from the improper handling of entity resolution within the SAX parser's event generation mechanism. When applications implement custom SAX handlers to control entity processing, they expect that setting the "checked" flag will prevent external entity content from being processed. However, the flaw in libxml2's implementation allows the parser to generate events for external entities regardless of these custom handler settings. This behavior creates a bypass condition where even when applications explicitly attempt to disable external entity processing, the parser continues to emit events for these entities, enabling attackers to craft malicious XML documents that trigger unintended processing behavior. The vulnerability is classified under CWE-611, which addresses Improper Restriction of XML External Entity Reference, and represents a classic case of insufficient input validation and access control.
The operational impact of CVE-2024-40896 is severe and far-reaching, as it enables classic XML External Entity (XXE) attacks that can lead to various security consequences. Attackers can exploit this vulnerability to perform server-side request forgery attacks, where the parser attempts to resolve external entities and potentially access internal network resources or external servers. The vulnerability also opens the door to local file inclusion attacks, where malicious XML documents can cause the parser to read local files on the server, potentially exposing sensitive system information. Additionally, this flaw can facilitate denial of service conditions by causing the parser to consume excessive resources when processing maliciously crafted XML documents. The vulnerability affects any application or system that relies on libxml2 for XML processing, including web applications, enterprise software, and security tools, making it a critical concern for organizations maintaining systems that process untrusted XML input.
Organizations should prioritize immediate remediation by upgrading to libxml2 versions 2.11.9, 2.12.9, or 2.13.3, which contain the necessary patches to address this vulnerability. System administrators should conduct comprehensive inventory checks to identify all systems running vulnerable versions of libxml2 and ensure proper patch management procedures are implemented. Additionally, defensive measures should include implementing proper XML input validation, disabling external entity processing at the application level, and employing web application firewalls to monitor and filter suspicious XML content. The ATT&CK framework categorizes this vulnerability under T1213 - Data from Information Repositories, as it enables unauthorized access to system resources through XML processing flaws, and T1068 - Exploitation for Privilege Escalation when the vulnerability leads to unauthorized access to sensitive files or resources. Security teams should also consider implementing monitoring and logging mechanisms to detect potential exploitation attempts targeting this vulnerability, as the attack surface extends to any application that processes XML input from untrusted sources.