Apache HTTP Server: HTTP request splitting with mod_rewrite and mod_proxy

Summary

Some mod_proxy configurations on Apache HTTP Server versions 2.4.0 through 2.4.55 allow a HTTP Request Smuggling attack. Configurations are affected when mod_proxy is enabled along with some form of RewriteRule or ProxyPassMatch in which a non-specific pattern matches some portion of the user-supplied request-target (URL) data and is then re-inserted into the proxied request-target using variable substitution. For example, something like: RewriteEngine on RewriteRule "^/here/(.*)" "http://example.com:8080/elsewhere?$1"; [P] ProxyPassReverse /here/ http://example.com:8080/ Request splitting/smuggling could result in bypass of access controls in the proxy server, proxying unintended URLs to existing origin servers, and cache poisoning. Users are recommended to update to at least version 2.4.56 of Apache HTTP Server.

Timeline

1. Mar 7, 2023, 3:09 PM UTCCVE published
2. Dec 18, 2025, 3:37 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: yes · Technical impact: total

3. Dec 18, 2025, 3:37 PM UTCRecord last updated
4. Oct 28, 2026EPSS reached 10%

   FIRST estimates at least a 10% chance of exploitation in the next 30 days

Affected versions

• Apache Software Foundation Apache HTTP Server

  From 2.4.0 · through 2.4.55

References 11