In irssi before 0.8.21, a NULL pointer dereference in the nickcmp function (CVE-2017-5193).
In irssi before 0.8.21, use after free when receiving invalid nick message (CVE-2017-5194).
In irssi before 0.8.21, out of bounds read in certain incomplete control codes (CVE-2017-5195).
In irssi before 0.8.21, out of bounds read in certain incomplete character sequences (CVE-2017-5196).
In irssi before 0.8.21, out of bounds read when printing certain values (CVE-2017-5356).