register.php in PunBB 1.2.10 allows remote attackers to cause an unspecified denial of service via a flood of new user registrations.
https://exchange.xforce.ibmcloud.com/vulnerabilities/24837
http://www.vupen.com/english/advisories/2006/0773
http://www.punbb.org/download/patch/punbb-1.2.10_to_1.2.11.patch