include/net/netfilter/nf_conntrack_extend.h in the netfilter subsystem in the Linux kernel before 3.14.5 uses an insufficiently large data type for certain extension data, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) via outbound network traffic that triggers extension loading, as demonstrated by configuring a PPTP tunnel in a NAT environment.
3.13.0-53.88