CVE-2026-93546: 
Apache HTTP Server vulnerability analysis and mitigation

CVE-2026-93546 is an integer overflow vulnerability in the mod_dav_fs module of Apache HTTP Server affecting all versions through 2.4.68. An authenticated WebDAV client with write access can exploit this flaw by sending PROPPATCH requests that declare an excessive number of XML namespaces, causing worker process crashes and persistent corruption of a directory's property database. The vulnerability was disclosed on October 1, 2026, and carries a CVSS v3.1 base score of 8.8 (High) (GitHub Advisory, Apache Advisory).

The root cause is an integer overflow or wraparound (CWE-190) in the mod_dav_fs module, which handles WebDAV filesystem operations. When processing PROPPATCH requests, the module fails to properly validate the number of XML namespace declarations, allowing an arithmetic overflow in an internal counter or buffer size calculation. This overflow can lead to memory corruption, crashing worker processes and permanently corrupting the directory property database (a persistent side effect beyond a simple crash). Exploitation requires network access and authenticated WebDAV write privileges, but no user interaction is needed (GitHub Advisory, Apache Advisory).

Successful exploitation results in a denial of service through repeated crashes of Apache worker processes, as well as persistent data integrity loss via corruption of the WebDAV directory property database. The combined confidentiality, integrity, and availability impact is rated High across all three dimensions in the CVSS scoring. While lateral movement potential is limited, the persistent corruption of the property database means recovery may require manual intervention beyond simply restarting the service (GitHub Advisory).

As of the disclosure date, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (GitHub Advisory). The NVD SSVC assessment classifies exploitation as "none" and notes the vulnerability is not automatable, as it requires authenticated WebDAV write access. The EPSS score is reported at 0.0, and the vulnerability does not appear in the CISA Known Exploited Vulnerabilities catalog. Exploitation is constrained to authenticated users with WebDAV write permissions, reducing the overall attack surface.

1. Reconnaissance: Identify Apache HTTP Server instances (version ≤ 2.4.68) with WebDAV enabled and write access permitted, using tools like Shodan, Censys, or manual HTTP OPTIONS requests to detect DAV headers.
2. Obtain credentials: Acquire valid WebDAV credentials with write access through phishing, credential stuffing, or other means, as authentication is required.
3. Craft malicious PROPPATCH request: Construct a WebDAV PROPPATCH HTTP request targeting a writable WebDAV directory, embedding an abnormally large number of XML namespace declarations in the request body to trigger the integer overflow.
4. Send the request: Transmit the crafted PROPPATCH request to the target server using a WebDAV client or tools such as curl with appropriate authentication headers.
5. Trigger overflow and crash: The excessive namespace count causes an integer overflow in mod_dav_fs, crashing one or more Apache worker processes and corrupting the directory's property database.
6. Repeat for sustained DoS: Resend the malicious request to continuously crash worker processes, causing persistent denial of service and compounding database corruption (GitHub Advisory, Apache Advisory).

• Network: Unusual or repeated HTTP PROPPATCH requests to WebDAV-enabled directories containing abnormally large XML bodies with excessive namespace declarations; high volume of PROPPATCH requests from a single authenticated client.
• Logs: Apache access logs showing repeated PROPPATCH requests returning 5xx error codes; Apache error logs recording worker process crashes (child pid ... exit signal Segmentation fault or similar) correlated with WebDAV activity.
• File System: Corruption or unexpected modification timestamps on WebDAV property database files (e.g., .DAV/ directory contents); inaccessible or malformed property database files in WebDAV-enabled directories.
• Process: Repeated unexpected termination and restart of Apache httpd worker processes visible in process monitoring or system logs.

Apache has released a patched version of Apache HTTP Server beyond 2.4.68; administrators should upgrade to the latest available release as the primary remediation (Apache Advisory, GitHub Advisory). As a workaround, restrict WebDAV write access (Dav On with write permissions) to only explicitly trusted and necessary clients using IP allowlists or strong authentication controls. Additionally, monitor and alert on anomalous PROPPATCH requests with excessive XML namespace declarations as a detection measure until patching is complete.