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.