CVE-2026-72251

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nfnatsip: reload possible stale data pointer

quoting sashiko:

 ------------------------------------------------------------------------

 [..] noticed a potential memory bug and header corruption involving the

 SIP NAT helper.

 In net/netfilter/nfnatsip.c:nfnatsip():

if (skbensurewritable(skb, skb->len)) {

nfcthelper_log(skb, ct, "cannot mangle packet");

return NF_DROP;

}

uh = (void *)skb->data + protoff;

uh->dest = ctsipinfo->forced_dport;

if (!nfnatmangleudppacket(skb, ct, ctinfo, protoff,

      0, 0, NULL, 0)) {

 If a cloned or fragmented SKB is reallocated by skbensurewritable(), the

 old data buffer is freed. However, nfnatsip() fails to update *dptr to

 point to the new buffer.

 It also appears to use nfnatmangleudppacket() on what could be a TCP

 packet, which would overwrite the sequence number with a checksum update.

 ------------------------------------------------------------------------

nfconntracksip linerizes skbs, hence no fragmented skb can be seen.

But clones are possible, so rebuild dptr.

Disable nfnatmangleudppacket() branch for TCP streams.

It doesn't look like this can ever happen, else we should have received

bug reports about this, so just check the conntrack is UDP and drop

otherwise.

The calling conntracksip set ->forceddport for SIPHDRVIA_UDP messages,

so I don't think this is ever expected to be true for a TCP stream.