The netjoin processing in Irssi 1.x before 1.0.2 allows attackers to cause a denial of service (use-after-free) and possibly execute arbitrary code via unspecified vectors.
https://irssi.org/security/irssi_sa_2017_03.txt
https://github.com/irssi/irssi/commit/77b2631c78461965bc9a7414aae206b5c514e1b3