A buffer overflow in iptables-restore in netfilter iptables 1.8.2 allows an attacker to (at least) crash the program or potentially gain code execution via a specially crafted iptables-save file. This is related to addparamtoargv in xshared.c.

It was reported [1] that iptables can allow protocols that do not have a protocol handler kernel module loaded.

Given following iptables ruleset: -P FORWARD DROP -A FORWARD -m sctp --dport 9 -j ACCEPT -A FORWARD -p tcp --dport 80 -j ACCEPT -A FORWARD -p tcp -m conntrack -m state ESTABLISHED,RELATED -j ACCEPT

One would assume that this allows SCTP on port 9 and TCP on port 80. Unfortunately, if the SCTP conntrack module is not loaded, this allows all SCTP communication to pass through, i.e. -p sctp -j ACCEPT

[1]: http://www.spinics.net/lists/netfilter-devel/msg33430.html