The FWDRV driver in Kerio Personal Firewall 4.2 and Server Firewall 1.1.1 allows local users to cause a denial of service (crash) by setting the PAGE_NOACCESS or PAGE_GUARD protection on the Page Environment Block (PEB), which triggers an exception, aka the "PEB lockout vulnerability."
http://www.securityfocus.com/bid/15094
http://www.kerio.com/security_advisory.html
http://securityreason.com/securityalert/78
http://secunia.com/advisories/17155
http://seclists.org/bugtraq/2005/Oct/166
http://pb.specialised.info/all/adv/kerio-fwdrv-dos-adv.txt
http://lists.grok.org.uk/pipermail/full-disclosure/2005-October/037958.html