The Apache HTTP server before 1.3.34, and 2.0.x before 2.0.55, when acting as an HTTP proxy, allows remote attackers to poison the web cache, bypass web application firewall protection, and conduct XSS attacks via an HTTP request with both a "Transfer-Encoding: chunked" header and a Content-Length header, which causes Apache to incorrectly handle and forward the body of the request in a way that causes the receiving server to process it as a separate HTTP request, aka "HTTP Request Smuggling."
http://www.mandriva.com/security/advisories?name=MDKSA-2005:130
http://www.debian.org/security/2005/dsa-805
http://www.debian.org/security/2005/dsa-803
http://support.avaya.com/elmodocs2/security/ASA-2006-081.htm
http://slackware.com/security/viewer.php?l=slackware-security&y=2005&m=slackware-security.600000
http://secunia.com/advisories/23074
http://secunia.com/advisories/19317
http://secunia.com/advisories/19185
http://secunia.com/advisories/19073
http://secunia.com/advisories/19072
http://secunia.com/advisories/17813
http://secunia.com/advisories/17487
http://secunia.com/advisories/17319
http://secunia.com/advisories/14530
http://seclists.org/lists/bugtraq/2005/Jun/0025.html
http://marc.info/?l=apache-httpd-announce&m=112931556417329&w=3