An issue was discovered in GNU Mailman before 2.1.28. A crafted URL can cause arbitrary text to be displayed on a web page from a trusted site.
https://www.mail-archive.com/mailman-users%40python.org/msg71003.html
https://usn.ubuntu.com/4348-1/
https://security.gentoo.org/glsa/201904-10
https://lists.debian.org/debian-lts-announce/2018/07/msg00034.html