Cross-site scripting (XSS) vulnerability in the web UI in Mailman before 2.1.26 allows remote attackers to inject arbitrary web script or HTML via a user-options URL.
http://packetstormsecurity.com/files/159761/Mailman-2.1.23-Cross-Site-Scripting.html
https://access.redhat.com/errata/RHSA-2018:0504
https://access.redhat.com/errata/RHSA-2018:0505
https://bugs.launchpad.net/mailman/+bug/1747209
https://lists.debian.org/debian-lts-announce/2018/02/msg00007.html