In Sophos Web Appliance (SWA) before 4.3.1.2, Session Fixation could occur, aka NSWA-1310.
https://community.sophos.com/products/web-appliance/b/blog/posts/release-of-swa-v4-3-1-2
http://www.securityfocus.com/bid/97261
http://wsa.sophos.com/rn/swa/concepts/ReleaseNotes_4.3.1.2.html