CVE-2013-4558 in Subversion
Summary
by MITRE
The get_parent_resource function in repos.c in mod_dav_svn Apache HTTPD server module in Subversion 1.7.11 through 1.7.13 and 1.8.1 through 1.8.4, when built with assertions enabled and SVNAutoversioning is enabled, allows remote attackers to cause a denial of service (assertion failure and Apache process abort) via a non-canonical URL in a request, as demonstrated using a trailing /.
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Analysis
by VulDB Data Team • 06/02/2021
The vulnerability identified as CVE-2013-4558 represents a critical denial of service flaw within the Apache HTTPD server module mod_dav_svn that affects specific versions of the Subversion software ecosystem. This issue manifests in the get_parent_resource function located within the repos.c file of the module, creating a scenario where remote attackers can exploit malformed URL structures to trigger assertion failures that ultimately result in Apache process termination. The vulnerability specifically impacts installations where assertions are enabled and SVNAutoversioning has been configured, making it particularly relevant for organizations maintaining robust version control systems with these particular configurations.
The technical exploitation mechanism relies on sending non-canonical URLs containing trailing slashes to the affected Apache server instances. When the mod_dav_svn module processes these malformed requests, the get_parent_resource function fails to properly handle the edge case presented by the trailing slash in the URL path. This failure causes an assertion to be triggered within the code execution flow, which when assertions are enabled in the build configuration, results in immediate program termination. The assertion failure essentially represents a fundamental breakdown in the module's input validation mechanisms, where the expected behavior of URL path handling does not align with the actual processing logic.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by attackers to systematically degrade the availability of version control services that depend on Apache with mod_dav_svn. Organizations utilizing Subversion repositories through Apache HTTPD servers face potential business continuity issues when this vulnerability is exploited, as the assertion failure causes complete Apache process crashes that require manual intervention to restore service. The vulnerability's exploitation requires minimal technical skill, making it particularly dangerous as it can be easily automated and used in large-scale attacks against multiple targets. From a cybersecurity perspective, this represents a classic example of how seemingly innocuous input validation issues can result in catastrophic service failures.
Mitigation strategies for CVE-2013-4558 focus primarily on updating to patched versions of Subversion that address the underlying assertion failure in the get_parent_resource function. Organizations should prioritize upgrading to Subversion versions 1.7.14, 1.8.5, or later releases that contain the appropriate code fixes. Additionally, administrators can implement temporary workarounds by disabling assertions in their Apache server configurations or by disabling SVNAutoversioning if it is not essential for their operations. The vulnerability aligns with CWE-617, which addresses reachable assertions, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should also implement monitoring solutions to detect unusual patterns of requests that might indicate exploitation attempts, particularly those involving malformed URLs with trailing slashes, as these patterns can serve as indicators of potential compromise within version control infrastructure.