In Open Ticket Request System (OTRS) 4.0.x before 4.0.32, 5.0.x before 5.0.30, and 6.0.x before 6.0.11, an attacker could send a malicious email to an OTRS system. If a logged in user opens it, the email could cause the browser to load external image or CSS resources.
https://www.debian.org/security/2018/dsa-4317
https://lists.debian.org/debian-lts-announce/2018/09/msg00033.html
https://github.com/OTRS/otrs/commit/baa92df09145b8ae2702a3a0e85d8ba55ec96302
https://github.com/OTRS/otrs/commit/a808859a75c59ae3b7568f5cc4708c53462aa4c7
https://github.com/OTRS/otrs/commit/09e80c7752b0d9080688e4597c7495dd109e0963
https://community.otrs.com/security-advisory-2018-05-security-update-for-otrs-framework/