A mailman security update has been released for both Debian GNU/Linux 9 and 10 to address a cross site scripting attack issue in mailman.

DSA 4664-1: mailman security update

- -------------------------------------------------------------------------
Debian Security Advisory DSA-4664-1 security@debian.org
  https://www.debian.org/security/ Thijs Kinkhorst
April 26, 2020   https://www.debian.org/security/faq
- -------------------------------------------------------------------------

Package : mailman
CVE ID : CVE-2020-12137

Hanno Boeck discovered that it was possible to create a cross site
scripting attack on the webarchives of the Mailman mailing list manager,
by sending a special type of attachement.

For the oldstable distribution (stretch), this problem has been fixed
in version 1:2.1.23-1+deb9u5.

For the stable distribution (buster), this problem has been fixed in
version 1:2.1.29-1+deb10u1.

We recommend that you upgrade your mailman packages.

For the detailed security status of mailman please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/mailman

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/