Ubuntu Security Notice 593-1 – It was discovered that the default configuration of dovecot could allow access to any email files with group “mail” without verifying that a user had valid rights. An attacker able to create symlinks in their mail directory could exploit this to read or delete another user’s email. By default, dovecot passed special characters to the underlying authentication systems. While Ubuntu releases of dovecot are not known to be vulnerable, the authentication routine was proactively improved to avoid potential future problems.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/64909/USN-593-1.txt
Source: https://packetstormsecurity.com/files/64909/Ubuntu-Security-Notice-593-1.html