Varnish is a web application accelerator.
Varnish fails to properly validate input from HTTP headers, and does not deny requests with multiple Content-Length headers.
Remote attackers could conduct an HTTP response splitting attack, which may further enable them to conduct Cross-Site Scripting (XSS), Cache Poisoning, Defacement, and Page Hijacking.
There is no known workaround at this time.
All Varnish users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=www-servers/varnish-3.0.7"