An issue was discovered in Irssi before 1.0.7 and 1.1.x before 1.1.1. Certain nick names could result in out-of-bounds access when printing theme strings.
http://openwall.com/lists/oss-security/2018/02/15/1
https://lists.debian.org/debian-lts-announce/2018/03/msg00021.html