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.
https://exchange.xforce.ibmcloud.com/vulnerabilities/16610
http://www.securityfocus.com/bid/10663
http://www.bandecon.com/advisory/unreal.txt