An issue was discovered in Open-Xchange OX Guard before 2.4.2-rev5. Script code which got injected to a mail with inline PGP signature gets executed when verifying the signature. Malicious script code can be executed within a user's context. This can lead to session hijacking or triggering unwanted actions via the web interface (sending mail, deleting data etc.).
https://www.exploit-db.com/exploits/40377/
https://euvd.enisa.europa.eu/vulnerability/EUVD-2016-7739
http://www.securityfocus.com/bid/92920
http://www.securityfocus.com/archive/1/539395/100/0/threaded
http://packetstormsecurity.com/files/138701/Open-Xchange-Guard-2.4.2-Cross-Site-Scripting.html