An issue was discovered in views/list.py in GNU Mailman Postorius before 1.3.5. An attacker (logged into any account) can send a crafted POST request to unsubscribe any user from a mailing list, also revealing whether that address was subscribed in the first place.
https://www.debian.org/security/2021/dsa-4970
https://phabricator.wikimedia.org/T289798
https://gitlab.com/mailman/postorius/-/tags
https://gitlab.com/mailman/postorius/-/issues/531
https://gitlab.com/mailman/postorius/-/commit/3d880c56b58bc26b32eac0799407d74b64b7474b