linux-cve-announce - CVE-2025-40206: netfilter: nft_objref: validate objref and objrefmap expressions

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Message-ID: <2025111247-CVE-2025-40206-b396@gregkh>
Date: Wed, 12 Nov 2025 17:01:09 -0500
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40206: netfilter: nft_objref: validate objref and objrefmap expressions

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

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

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

netfilter: nft_objref: validate objref and objrefmap expressions

Referencing a synproxy stateful object from OUTPUT hook causes kernel
crash due to infinite recursive calls:

BUG: TASK stack guard page was hit at 000000008bda5b8c (stack is 000000003ab1c4a5..00000000494d8b12)
[...]
Call Trace:
 __find_rr_leaf+0x99/0x230
 fib6_table_lookup+0x13b/0x2d0
 ip6_pol_route+0xa4/0x400
 fib6_rule_lookup+0x156/0x240
 ip6_route_output_flags+0xc6/0x150
 __nf_ip6_route+0x23/0x50
 synproxy_send_tcp_ipv6+0x106/0x200
 synproxy_send_client_synack_ipv6+0x1aa/0x1f0
 nft_synproxy_do_eval+0x263/0x310
 nft_do_chain+0x5a8/0x5f0 [nf_tables
 nft_do_chain_inet+0x98/0x110
 nf_hook_slow+0x43/0xc0
 __ip6_local_out+0xf0/0x170
 ip6_local_out+0x17/0x70
 synproxy_send_tcp_ipv6+0x1a2/0x200
 synproxy_send_client_synack_ipv6+0x1aa/0x1f0
[...]

Implement objref and objrefmap expression validate functions.

Currently, only NFT_OBJECT_SYNPROXY object type requires validation.
This will also handle a jump to a chain using a synproxy object from the
OUTPUT hook.

Now when trying to reference a synproxy object in the OUTPUT hook, nft
will produce the following error:

synproxy_crash.nft: Error: Could not process rule: Operation not supported
  synproxy name mysynproxy
  ^^^^^^^^^^^^^^^^^^^^^^^^

The Linux kernel CVE team has assigned CVE-2025-40206 to this issue.


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

	Issue introduced in 5.4 with commit ee394f96ad7517fbc0de9106dcc7ce9efb14f264 and fixed in 6.6.113 with commit 0028e0134c64d9ed21728341a74fcfc59cd0f944
	Issue introduced in 5.4 with commit ee394f96ad7517fbc0de9106dcc7ce9efb14f264 and fixed in 6.12.54 with commit 7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0
	Issue introduced in 5.4 with commit ee394f96ad7517fbc0de9106dcc7ce9efb14f264 and fixed in 6.17.4 with commit 4c1cf72ec10be5a9ad264650cadffa1fbce6fabd
	Issue introduced in 5.4 with commit ee394f96ad7517fbc0de9106dcc7ce9efb14f264 and fixed in 6.18-rc1 with commit f359b809d54c6e3dd1d039b97e0b68390b0e53e4

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-2025-40206
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/nft_objref.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/0028e0134c64d9ed21728341a74fcfc59cd0f944
	https://git.kernel.org/stable/c/7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0
	https://git.kernel.org/stable/c/4c1cf72ec10be5a9ad264650cadffa1fbce6fabd
	https://git.kernel.org/stable/c/f359b809d54c6e3dd1d039b97e0b68390b0e53e4