CVE-2026-72251: netfilter: nf_nat_sip: reload possible stale data pointer

CVE-2026-72251: netfilter: nf_nat_sip: reload possible stale data pointer

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

netfilter: nf_nat_sip: reload possible stale data pointer

quoting sashiko:
 ------------------------------------------------------------------------
 [..] noticed a potential memory bug and header corruption involving the
 SIP NAT helper.

 In net/netfilter/nf_nat_sip.c:nf_nat_sip():
	if (skb_ensure_writable(skb, skb->len)) {
		nf_ct_helper_log(skb, ct, "cannot mangle packet");
		return NF_DROP;
	}
	uh = (void *)skb->data + protoff;
	uh->dest = ct_sip_info->forced_dport;
	if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, protoff,
				      0, 0, NULL, 0)) {

 If a cloned or fragmented SKB is reallocated by skb_ensure_writable(), the
 old data buffer is freed. However, nf_nat_sip() fails to update *dptr to
 point to the new buffer.

 It also appears to use nf_nat_mangle_udp_packet() on what could be a TCP
 packet, which would overwrite the sequence number with a checksum update.
 ------------------------------------------------------------------------

nf_conntrack_sip linerizes skbs, hence no fragmented skb can be seen.
But clones are possible, so rebuild dptr.

Disable nf_nat_mangle_udp_packet() 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 conntrack_sip set ->forced_dport for SIP_HDR_VIA_UDP messages,
so I don't think this is ever expected to be true for a TCP stream.

The Linux kernel CVE team has assigned CVE-2026-72251 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 5.10.261 with commit bded21a4bf9bf86a79148be735723a97ca9a7532
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 5.15.212 with commit dc11f26685aa850f237226f0f463647aea58ab7c
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 6.1.178 with commit e38143c9b477f2968024c47c647dd4456a40aff1
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 6.6.145 with commit 57e4e29644ec054d7021d296407e7ddd844afea2
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 6.12.97 with commit eae9c6ccb5af69c713a65f8ae219f5c1aa32cd17
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 6.18.40 with commit 2bcf2c5052fb5e73e255140ab43f056aef409c27
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 7.1.5 with commit 0e76e3e886cc9ee027337d5ad39cb96f57b7bdc7
	Issue introduced in 3.9 with commit 7266507d89991fa1e989283e4e032c6d9357fe26 and fixed in 7.2-rc3 with commit 77e43bcb7ec177e293a5c3f1b91a2c5aebfb6c68

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-72251
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/netfilter/nf_nat_sip.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/bded21a4bf9bf86a79148be735723a97ca9a7532
	https://git.kernel.org/stable/c/dc11f26685aa850f237226f0f463647aea58ab7c
	https://git.kernel.org/stable/c/e38143c9b477f2968024c47c647dd4456a40aff1
	https://git.kernel.org/stable/c/57e4e29644ec054d7021d296407e7ddd844afea2
	https://git.kernel.org/stable/c/eae9c6ccb5af69c713a65f8ae219f5c1aa32cd17
	https://git.kernel.org/stable/c/2bcf2c5052fb5e73e255140ab43f056aef409c27
	https://git.kernel.org/stable/c/0e76e3e886cc9ee027337d5ad39cb96f57b7bdc7
	https://git.kernel.org/stable/c/77e43bcb7ec177e293a5c3f1b91a2c5aebfb6c68