XSS on Apache HTTP Server 413 error pages via malformed HTTP method

Description

Apache HTTP Server versions prior to the patched releases contain a cross-site scripting (XSS) vulnerability in the error handling mechanism for HTTP 413 (Request Entity Too Large) responses. When the server receives a malformed HTTP method combined with an oversized request, it reflects the malicious method name directly into the error page without proper sanitization. Attackers can exploit this by crafting requests with JavaScript payloads embedded in the HTTP method field, which will execute in victims' browsers when they are tricked into triggering the error condition.

Remediation

Upgrade Apache HTTP Server to a patched version that addresses CVE-2007-6203. Specifically, upgrade to Apache 2.2.8 or later for the 2.2.x branch, or Apache 2.0.63 or later for the 2.0.x branch. If immediate patching is not feasible, implement the following interim mitigations:

1. Deploy a Web Application Firewall (WAF) or reverse proxy to filter requests with malformed HTTP methods before they reach Apache
2. Configure custom error pages that do not reflect user input
3. Implement Content Security Policy (CSP) headers to restrict inline script execution
4. Monitor server logs for requests with unusually long or non-standard HTTP methods

After upgrading, verify the patch by testing with a malformed method request and confirming that the error page properly sanitizes or omits the method name from the response.