qpopper POP server creates lock files with predictable names, which allows local users to cause a denial of service for other users (lack of mail access) by creating lock files for other mail boxes.

Qpopper 2.53 and earlier allows local users to gain privileges via a formatting string in the From: header, which is processed by the euidl command.

Qpopper 2.53 and 3.0 does not properly identify the \n string which identifies the end of message text, which allows a remote attacker to cause a denial of service or corrupt mailboxes via a message line that is 1023 characters long and ends in \n.