CVE-2008-4409 in libxml2
Summary
by MITRE
libxml2 2.7.0 and 2.7.1 does not properly handle "predefined entities definitions" in entities, which allows context-dependent attackers to cause a denial of service (memory consumption and application crash), as demonstrated by use of xmllint on a certain XML document, a different vulnerability than CVE-2003-1564 and CVE-2008-3281.
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Analysis
by VulDB Data Team • 12/25/2025
The vulnerability identified as CVE-2008-4409 affects libxml2 versions 2.7.0 and 2.7.1, specifically targeting the library's handling of predefined entity definitions within XML documents. This issue represents a significant security concern as it enables context-dependent attackers to exploit memory consumption patterns and potentially cause application crashes through carefully crafted XML input. The flaw manifests when the xmllint utility processes certain XML documents that contain malformed entity definitions, creating a denial of service condition that can severely impact systems relying on libxml2 for XML processing. Unlike similar vulnerabilities such as CVE-2003-1564 and CVE-2008-3281, this particular weakness stems from the library's improper handling of entity definitions rather than other aspects of XML parsing.
The technical root cause of this vulnerability lies in libxml2's insufficient validation and processing of predefined entity definitions within XML documents. When the library encounters XML content containing maliciously constructed entity references, it fails to properly manage memory allocation during the parsing process. This improper handling results in excessive memory consumption that can lead to system resource exhaustion, ultimately causing the application to crash or become unresponsive. The vulnerability specifically impacts how the library processes entity definitions that reference predefined entities, creating a scenario where recursive or deeply nested entity references can cause memory allocation to spiral out of control without proper bounds checking or termination conditions.
From an operational impact perspective, this vulnerability poses a substantial risk to systems that utilize libxml2 for XML processing, particularly those handling untrusted input from external sources. Applications that process XML documents through xmllint or other libxml2-based tools become susceptible to denial of service attacks, where an attacker can craft malicious XML documents to consume excessive system resources. The vulnerability can be exploited in web applications, XML processing services, and any system that relies on libxml2 for parsing XML content, potentially leading to service disruption and availability issues that can affect business operations and user access to critical services.
Security mitigations for CVE-2008-4409 should focus on immediate remediation through version updates, with organizations upgrading to libxml2 versions that contain the necessary patches addressing the entity definition handling flaw. System administrators should implement input validation measures to filter or sanitize XML content before processing, particularly when dealing with untrusted sources. Additionally, deploying application firewalls or intrusion prevention systems that can detect and block malicious XML patterns may provide additional protection layers. Organizations should also consider implementing resource limits and monitoring mechanisms to detect unusual memory consumption patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-400, which addresses improper resource management in software systems, and may be mapped to ATT&CK technique T1499.004 for denial of service via resource exhaustion attacks.