In Irssi before 1.0.3, when receiving a DCC message without source nick/host, it attempts to dereference a NULL pointer. Thus, remote IRC servers can cause a crash.
https://irssi.org/security/irssi_sa_2017_06.txt
http://www.securitytracker.com/id/1038621
http://www.securityfocus.com/bid/99015