Ubuntu Security Notice 288-4 – USN-288-3 fixed a vulnerability in dovecot. Unfortunately the Ubuntu 6.06 update had a regression which caused authentication using a MySQL database to not work any more. This update fixes this again.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/47532/USN-288-4.txt
Source: https://packetstormsecurity.com/files/47532/Ubuntu-Security-Notice-288-4.html