In the Linux kernel, the following vulnerability has been resolved:
netfilter: xt_nat: reject unsupported target families
xt_nat SNAT and DNAT target handlers assume IP-family conntrack state
is present and can dereference a NULL pointer when instantiated from an
unsupported family through nft_compat. A bridge-family compat rule can
therefore trigger a NULL-dereference in nf_nat_setup_info().
Reject non-IP families in xt_nat_checkentry() so unsupported targets
cannot be installed. Keep NFPROTO_INET allowed for valid inet NAT
compat users and leave the runtime fast path unchanged.
[ The crash was fixed via
9dbba7e694ec (“netfilter: nft_compat: ebtables emulation must reject non-bridge targets”),
so this patch is no longer critical.
Nevertheless, NAT is only relevant for ipv4/ipv6, so this extra
family check is a good idea in any case. ]
