This update for mailman to version 2.1.15 fixes the following issues:
CVE-2016-6893: Prevent cross-site request forgery (CSRF) vulnerability in the
user options page that allowed remote attackers to hijack the authentication of
arbitrary users for requests that modify an option (bsc#995352).
Various other hardenings against CSFR attacks
For details please see https://launchpad.net/mailman/+milestone/2.1.15