linux-cve-announce - CVE-2025-71160: netfilter: nf_tables: avoid chain re-validation if possible

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Message-ID: <2026012346-CVE-2025-71160-8c5d@gregkh>
Date: Fri, 23 Jan 2026 16:24:47 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71160: netfilter: nf_tables: avoid chain re-validation if possible

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

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

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

netfilter: nf_tables: avoid chain re-validation if possible

Hamza Mahfooz reports cpu soft lock-ups in
nft_chain_validate():

 watchdog: BUG: soft lockup - CPU#1 stuck for 27s! [iptables-nft-re:37547]
[..]
 RIP: 0010:nft_chain_validate+0xcb/0x110 [nf_tables]
[..]
  nft_immediate_validate+0x36/0x50 [nf_tables]
  nft_chain_validate+0xc9/0x110 [nf_tables]
  nft_immediate_validate+0x36/0x50 [nf_tables]
  nft_chain_validate+0xc9/0x110 [nf_tables]
  nft_immediate_validate+0x36/0x50 [nf_tables]
  nft_chain_validate+0xc9/0x110 [nf_tables]
  nft_immediate_validate+0x36/0x50 [nf_tables]
  nft_chain_validate+0xc9/0x110 [nf_tables]
  nft_immediate_validate+0x36/0x50 [nf_tables]
  nft_chain_validate+0xc9/0x110 [nf_tables]
  nft_immediate_validate+0x36/0x50 [nf_tables]
  nft_chain_validate+0xc9/0x110 [nf_tables]
  nft_table_validate+0x6b/0xb0 [nf_tables]
  nf_tables_validate+0x8b/0xa0 [nf_tables]
  nf_tables_commit+0x1df/0x1eb0 [nf_tables]
[..]

Currently nf_tables will traverse the entire table (chain graph), starting
from the entry points (base chains), exploring all possible paths
(chain jumps).  But there are cases where we could avoid revalidation.

Consider:
1  input -> j2 -> j3
2  input -> j2 -> j3
3  input -> j1 -> j2 -> j3

Then the second rule does not need to revalidate j2, and, by extension j3,
because this was already checked during validation of the first rule.
We need to validate it only for rule 3.

This is needed because chain loop detection also ensures we do not exceed
the jump stack: Just because we know that j2 is cycle free, its last jump
might now exceed the allowed stack size.  We also need to update all
reachable chains with the new largest observed call depth.

Care has to be taken to revalidate even if the chain depth won't be an
issue: chain validation also ensures that expressions are not called from
invalid base chains.  For example, the masquerade expression can only be
called from NAT postrouting base chains.

Therefore we also need to keep record of the base chain context (type,
hooknum) and revalidate if the chain becomes reachable from a different
hook location.

The Linux kernel CVE team has assigned CVE-2025-71160 to this issue.

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

	Fixed in 6.6.121 with commit 53de1e6cde8f9b791d9cf61aa0e7b02cf5bbe8b1
	Fixed in 6.12.66 with commit 14fa3d1927f1382f86e3f70a51f26005c8e3cff6
	Fixed in 6.18.6 with commit 09d6074995c186e449979fe6c1b0f1a69cf9bd3b
	Fixed in 6.19-rc2 with commit 8e1a1bc4f5a42747c08130b8242ebebd1210b32f

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-2025-71160
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:
	include/net/netfilter/nf_tables.h
	net/netfilter/nf_tables_api.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/53de1e6cde8f9b791d9cf61aa0e7b02cf5bbe8b1
	https://git.kernel.org/stable/c/14fa3d1927f1382f86e3f70a51f26005c8e3cff6
	https://git.kernel.org/stable/c/09d6074995c186e449979fe6c1b0f1a69cf9bd3b
	https://git.kernel.org/stable/c/8e1a1bc4f5a42747c08130b8242ebebd1210b32f