source: http://www.securityfocus.com/bid/9794/info

1st Class Mail Server has been reported prone to a remote buffer overflow vulnerability. The issue exists due to a lack of sufficient boundary checks performed on user-supplied data.

A remote attacker may pass excessive data as an argument for an APOP command passed to the affected server. The attacker may exploit this issue to corrupt a saved instruction pointer and in doing so may potentially influence execution flow of the affected service into attacker-supplied instructions.

APOP user AAAA ... [626 * A] ... AAAA