The (1) Conn_StartLogin and (2) cb_Read_Resolver_Result 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 Handle_Write 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.