The (1) ConnStartLogin and (2) cbReadResolverResult functions in conn.c in ngIRCd 18 through 20.2, when the configuration option NoticeAuth is enabled, does not properly handle the return code for the HandleWrite function, which allows remote attackers to cause a denial of service (assertion failure and server crash) via unspecified vectors, related to a "notice auth" message not being sent to a new client.

ngIRCd 0.10.x before 0.10.4 and 0.11.0 before 0.11.0-pre2 allows remote attackers to cause a denial of service (crash) via crafted IRC PART message, which triggers an invalid dereference.

channel.c in ngIRCd 20 and 20.1 allows remote attackers to cause a denial of service (assertion failure and crash) via a KICK command for a user who is not on the associated channel.

The Server-Server protocol implementation in ngIRCd before 26~rc2 allows an out-of-bounds access, as demonstrated by the IRCNJOIN() function.