Apache HTTP Server Security Advisory ==================================== Title: mod_proxy reverse proxy exposure CVE: CVE-2011-3368 Date: 20111005 Product: Apache HTTP Server Versions: httpd 1.3 all versions, httpd 2.x all versions Description: ============ An exposure was reported affecting the use of Apache HTTP Server in reverse proxy mode. We would like to thank Context Information Security Ltd for reporting this issue to us. When using the RewriteRule or ProxyPassMatch directives to configure a reverse proxy using a pattern match, it is possible to inadvertently expose internal servers to remote users who send carefully crafted requests. The server did not validate that the input to the pattern match was a valid path string, so a pattern could expand to an unintended target URL. For future releases of the Apache HTTP Server, the software will validate the request URI, correcting this specific vulnerability. The documentation has been updated to reflect the more general risks with pattern matching in a reverse proxy configuration. Details: ======== A configuration like one of the following examples: RewriteRule (.*)\.(jpg|gif|png) http://images.example.com$1.$2 [P] ProxyPassMatch (.*)\.(jpg|gif|png) http://images.example.com$1.$2 could result in an exposure of internal servers. A request of the form: GET @other.example.com/something.png HTTP/1.1 would get translated to a target of: http://email@example.com/s... This will cause the proxy to connect to the hostname "other.example.com", as the "images.example.com@" segment would be treated as user credentials when parsing the URL. This would allow a remote attacker the ability to proxy to hosts other than those expected, which could be a security exposure in some circumstances. The request-URI string in this example, "@other.example.com/something.png", is not valid according to the HTTP specification, since it neither an absolute URI ("http://example.com/path") nor an absolute path ("/path"). For future releases, the server has been patched to reject such requests, instead returning a "400 Bad Request" error. Actions: ======== Apache HTTPD users should examine their configuration files to determine if they have used an insecure configuration for reverse proxying. Affected users can update their configuration, or apply the patch from: http://www.apache.org/dist/httpd/patches/appl... For example, the above RewriteRule could be changed to: RewriteRule /(.*)\.(jpg|gif|png) http://images.example.com/$1.$2 [P] to ensure the pattern only matches against paths with a leading "/".