isakmpd in OpenBSD 3.4 and earlier allows remote attackers to cause a denial of service via an ISAKMP packet with a malformed Cert Request payload, which causes an integer underflow that is used in a malloc operation that is not properly handled, as demonstrated by the Striker ISAKMP Protocol Test Suite.
https://exchange.xforce.ibmcloud.com/vulnerabilities/15629
http://www.securitytracker.com/alerts/2004/Mar/1009468.html
http://www.securityfocus.com/bid/9907
http://www.openbsd.org/errata.html