net/netfilter/nf_conntrack_proto_generic.c in the Linux kernel before 3.18 generates incorrect conntrack entries during handling of certain iptables rule sets for the SCTP, DCCP, GRE, and UDP-Lite protocols, which allows remote attackers to bypass intended access restrictions via packets with disallowed port numbers.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.