The Server-Server protocol implementation in ngIRCd before 26~rc2 allows an out-of-bounds access, as demonstrated by the IRC_NJOIN() function.
https://lists.debian.org/debian-lts-announce/2020/06/msg00023.html
https://github.com/ngircd/ngircd/releases/tag/rel-26-rc2
https://github.com/ngircd/ngircd/pull/276
https://github.com/ngircd/ngircd/pull/275