The proxy engine on Cisco Web Security Appliance (WSA) devices with software 8.5.3-055, 9.1.0-000, and 9.5.0-235 allows remote attackers to bypass intended proxy restrictions via a malformed HTTP method, aka Bug ID CSCux00848.
http://www.securitytracker.com/id/1034763
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160119-wsa