Debian Security Advisory DSA 917-1 – Patrick Cheong Shu Yang discovered that courier-authdaemon, the authentication daemon of the Courier Mail Server, grants access to accounts that are already deactivated.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/42249/dsa-917-1.txt
Source: https://packetstormsecurity.com/files/42249/Debian-Linux-Security-Advisory-917-1.html