The try_parse_v4_netmask function in hostmask.c in IRCD-Hybrid before 8.0.6 does not properly validate masks, which allows remote attackers to cause a denial of service (crash) via a mask that causes a negative number to be parsed.
https://wiki.mageia.org/en/Support/Advisories/MGASA-2013-0055
https://exchange.xforce.ibmcloud.com/vulnerabilities/81695
http://www.securityfocus.com/bid/57610
http://www.openwall.com/lists/oss-security/2013/01/29/8
http://www.mandriva.com/security/advisories?name=MDVSA-2013:093
http://www.exploit-db.com/exploits/24951
http://www.debian.org/security/2013/dsa-2618
http://secunia.com/advisories/52106