ircII before 20210314 allows remote attackers to cause a denial of service (segmentation fault and client crash, disconnecting the victim from an IRC server) via a crafted CTCP UTC message.
https://www.openwall.com/lists/oss-security/2021/03/24/2
https://lists.debian.org/debian-lts-announce/2021/08/msg00023.html
https://lists.debian.org/debian-lts-announce/2021/08/msg00022.html