UnrealIRCd 3.2.3 allows remote attackers to cause an unspecified denial of service by causing a linked server to send malformed TKL Q:Line commands, as demonstrated by "TKL - q\x08Q *\x08PoC."
The IP cloaking feature (cloak.c) in UnrealIRCd 3.2, and possibly other versions, uses a weak hashing scheme to hide IP addresses, which could allow remote attackers to use brute force methods to gain other user's IP addresses.
Format string vulnerability in the Cio_PrintF function of cio_main.c in Unreal IRCd 3.1.1 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via format string specifiers.