CVE-2018-11803 in Subversion
Summary
by MITRE
Subversion's mod_dav_svn Apache HTTPD module versions 1.11.0 and 1.10.0 to 1.10.3 will crash after dereferencing an uninitialized pointer if the client omits the root path in a recursive directory listing operation.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/06/2023
The vulnerability identified as CVE-2018-11803 affects the mod_dav_svn Apache HTTPD module within Subversion version 1.11.0 and the 1.10.0 through 1.10.3 release series. This issue represents a critical software flaw that manifests when the module processes recursive directory listing operations from clients that fail to provide the required root path parameter. The problem stems from the module's improper handling of uninitialized memory pointers during the processing of these specific requests, creating a condition where the software attempts to access memory locations that have not been properly initialized. The vulnerability is particularly concerning because it allows for a denial of service condition that can completely crash the Apache HTTPD server, rendering the version control service unavailable to legitimate users.
The technical implementation of this flaw involves the mod_dav_svn module's internal processing logic for handling WebDAV requests related to directory listings. When a client submits a recursive directory listing request without specifying the root path, the module's code path fails to properly initialize a pointer variable before attempting to dereference it. This uninitialized pointer typically contains garbage data from previous memory operations, causing the application to attempt to access invalid memory addresses. The vulnerability is categorized under CWE-476 as a NULL pointer dereference, though in this specific case it involves an uninitialized pointer rather than a null one. The crash occurs during the normal operation of the WebDAV protocol implementation, specifically when processing the DAV:propfind and DAV:multistatus responses that are part of the standard WebDAV communication pattern.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides an attacker with a reliable method to cause persistent denial of service against Subversion repositories hosted on affected Apache servers. The crash condition is triggered by a specific client request pattern that does not require any authentication or special privileges, making it particularly dangerous in environments where the Subversion server is publicly accessible or where untrusted users have access to the repository. The vulnerability affects the core functionality of the Apache HTTPD server's WebDAV module, which is commonly used for collaborative software development environments where version control repositories are exposed through HTTP interfaces. This makes the impact widespread across organizations using Subversion in web-accessible configurations, particularly those that rely on the mod_dav_svn module for repository access. The vulnerability also aligns with ATT&CK technique T1499.004 for network denial of service, as it allows an attacker to disrupt network services through the deliberate exploitation of software flaws.
Organizations affected by this vulnerability should immediately implement mitigations including updating to Subversion versions 1.10.4 or 1.11.1, which contain the necessary patches to properly initialize the affected pointer variables. Additionally, administrators should consider implementing access controls to restrict WebDAV access to trusted clients only, particularly when the vulnerability cannot be immediately patched. Network monitoring should be enhanced to detect and alert on unusual patterns of directory listing requests that may indicate exploitation attempts. The patch implementation should be validated through thorough testing in staging environments to ensure that the fix does not introduce regressions in other functionality. Security teams should also review their incident response procedures to ensure they can quickly identify and respond to service disruption events that may be related to this vulnerability. Organizations using Subversion in high-availability environments should consider implementing redundant repository access methods and failover procedures to minimize the impact of potential exploitation attempts.