Apache HTTP Server: mod_proxy reverse proxy exposure

http://seclists.org/fulldisclosure/2011/Oct/232

"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."