CVE-2013-6438 in MacOS X
Summary
by MITRE
The dav_xml_get_cdata function in main/util.c in the mod_dav module in the Apache HTTP Server before 2.4.8 does not properly remove whitespace characters from CDATA sections, which allows remote attackers to cause a denial of service (daemon crash) via a crafted DAV WRITE request.
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Analysis
by VulDB Data Team • 05/08/2026
The vulnerability identified as CVE-2013-6438 resides within the mod_dav module of the Apache HTTP Server version 2.4.7 and earlier, specifically in the dav_xml_get_cdata function located in main/util.c. This flaw represents a classic buffer manipulation issue that exploits improper handling of XML CDATA sections during WebDAV operations. The vulnerability manifests when the server processes DAV WRITE requests containing specially crafted XML content that includes whitespace characters within CDATA sections. The root cause stems from insufficient sanitization of XML data structures, allowing malformed input to bypass normal validation mechanisms and potentially corrupt memory structures within the Apache daemon process.
The technical exploitation of this vulnerability occurs through a carefully constructed DAV WRITE request that includes malformed CDATA sections with specific whitespace character sequences. When the dav_xml_get_cdata function processes these inputs, it fails to properly strip or normalize whitespace characters that should be removed from CDATA content according to XML standards. This improper handling creates a memory corruption scenario where the daemon's internal data structures become compromised, leading to unpredictable behavior and ultimately resulting in a daemon crash. The vulnerability operates at the XML parsing layer within the WebDAV module, making it particularly dangerous as it can be triggered through standard HTTP WebDAV operations without requiring authentication or special privileges beyond basic web access.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attack vectors. While the primary effect is a denial of service condition that crashes the Apache daemon, the underlying memory corruption could theoretically be exploited to achieve arbitrary code execution under certain conditions, though this would require additional attack surface exploitation. The vulnerability affects all versions of Apache HTTP Server prior to 2.4.8, making it particularly concerning for organizations running legacy installations. The impact is significant because Apache serves as the foundation for countless web applications and services, and a daemon crash can result in complete service unavailability for affected systems.
Organizations should prioritize immediate patching to address this vulnerability, as the Apache HTTP Server 2.4.8 and later versions contain the necessary fixes that properly sanitize CDATA sections and normalize whitespace characters. The mitigation strategy should include comprehensive testing of the updated Apache installations to ensure no regression in functionality, particularly for WebDAV-enabled services. System administrators should also implement network-level monitoring to detect unusual DAV WRITE request patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing web application firewalls or intrusion detection systems that can identify and block malformed XML content attempting to exploit this specific vulnerability. This remediation aligns with industry best practices for vulnerability management and follows the principles outlined in the CWE-129 category for improper input validation and the ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the critical need for proper input sanitization and robust error handling in web server components.