mystring.c in hybserv in IRCD-Hybrid (aka Hybrid2 IRC Services) 1.9.2 through 1.9.4 allows remote attackers to cause a denial of service (daemon crash) via a ":help \t" private message to the MemoServ service.
https://exchange.xforce.ibmcloud.com/vulnerabilities/55992
http://www.securityfocus.com/bid/38006
http://www.debian.org/security/2010/dsa-1982
http://security.debian.org/pool/updates/main/h/hybserv/hybserv_1.9.2-4+lenny2.diff.gz
http://secunia.com/advisories/38352
http://secunia.com/advisories/38350