CVE-2016-6312 in Subversion
Summary
by MITRE
The mod_dontdothat component of the mod_dav_svn Apache module in Subversion as packaged in Red Hat Enterprise Linux 5.11 does not properly detect recursion during entity expansion, which allows remote authenticated users with access to the webdav repository to cause a denial of service (memory consumption and httpd crash). NOTE: Exists as a regression to CVE-2009-1955.
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Analysis
by VulDB Data Team • 01/01/2021
The vulnerability described in CVE-2016-6312 represents a critical denial of service weakness within the Apache Subversion module ecosystem, specifically affecting the mod_dav_svn component in Red Hat Enterprise Linux 5.11. This issue manifests as a recursive entity expansion flaw that occurs during WebDAV repository operations, creating a scenario where authenticated users can exploit the system's processing mechanisms to consume excessive memory resources. The vulnerability serves as a regression to the previously addressed CVE-2009-1955, indicating that a similar weakness was re-introduced or inadequately fixed in the subsequent software version, highlighting the persistent nature of recursive processing vulnerabilities in web-based repository systems.
The technical flaw within mod_dontdothat component stems from inadequate recursion detection during XML entity expansion processes. When an authenticated user submits maliciously crafted WebDAV requests containing recursive entity references, the module fails to properly monitor or limit the depth of entity expansion. This allows the system to enter an infinite recursion loop where XML entities repeatedly reference themselves, causing exponential memory consumption patterns that ultimately lead to httpd process crashes. The vulnerability specifically targets the mod_dav_svn module's handling of WebDAV protocol operations, making it particularly dangerous in environments where repository access is granted to authenticated users, as the attack requires only legitimate access rights to trigger the denial of service condition.
From an operational impact perspective, this vulnerability creates significant risks for organizations relying on Apache Subversion repositories for version control and collaborative development. The memory consumption pattern can quickly exhaust available system resources, leading to complete service unavailability for legitimate users while potentially causing cascading failures across dependent systems. The fact that the attack requires only authenticated access makes it particularly concerning as it can be exploited by insiders or compromised accounts, and the crash condition affects the entire httpd service rather than individual repository operations. Organizations may experience extended downtime, productivity losses, and potential data access interruptions that can severely impact development workflows and business continuity.
The mitigation strategies for CVE-2016-6312 should focus on immediate patching of affected systems and implementation of additional protective measures. Organizations must apply the relevant security updates provided by Red Hat to address the specific recursion detection flaw in mod_dav_svn. Network-level protections should include implementing rate limiting and resource monitoring for WebDAV endpoints to detect unusual memory consumption patterns. Additionally, administrative controls should enforce strict access controls and monitoring of repository activities, particularly for authenticated users who have WebDAV access. The vulnerability aligns with CWE-400, which addresses unchecked resource consumption, and relates to ATT&CK technique T1499.004 for network denial of service, emphasizing the need for comprehensive defensive measures that address both the immediate technical flaw and broader security posture considerations.
This vulnerability demonstrates the persistent challenges in managing recursive processing and entity expansion in web-based systems, particularly in version control and repository environments. The regression nature of the issue indicates that security fixes must be carefully validated and monitored to prevent similar weaknesses from re-emerging in updated software versions. Organizations should implement robust testing procedures for security patches, particularly for modules handling XML processing and WebDAV protocols, to ensure that recursion detection mechanisms remain effective against evolving attack vectors while maintaining the functionality required for legitimate repository operations.