Irssi 1.3.x and 1.4.x before 1.4.4 has a use-after-free because of use of a stale special collector reference. This occurs when printing of a non-formatted line is concurrent with printing of a formatted line.
Ubuntu Security Notice 6002-1 - It was discovered that Irssi incorrectly handled certain internal routines. An attacker could possibly use this issue to cause a crash.