ip_nat_pptp in the PPTP NAT helper (netfilter/ip_nat_helper_pptp.c) in Linux kernel 2.6.14, and other versions, allows remote attackers to cause a denial of service (memory corruption or crash) via an inbound PPTP_IN_CALL_REQUEST packet that causes a null pointer to be used in an offset calculation.
kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commitdiff%3Bh=15db34702cfafd24acc60295cf14861e497502ab
secunia.com/advisories/18482
securityreason.com/securityalert/388
www.securityfocus.com/bid/16414
www.trustix.org/errata/2006/0004
www.vupen.com/english/advisories/2006/0220
exchange.xforce.ibmcloud.com/vulnerabilities/24203