From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-80978: net: cap advertised IP tunnel headroom
Date: Fri, 11 Sep 2026 21:41:24 +0200 [thread overview]
Message-ID: <2026091146-CVE-2026-80978-10ac@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
net: cap advertised IP tunnel headroom
IP tunnel devices derive their advertised needed_headroom from lower
output devices. A stack of user-created devices can make the derived
value larger than the 16-bit skb header offsets can represent. Once IP
output reserves it, skb head expansion can wrap those offsets.
The runtime transmit path already caps a growing needed_headroom at 512.
Apply the same cap when tunnel configuration publishes needed_headroom
derived from a lower output device.
Capping the advertised value is safe: IP tunnel transmit still expands
the skb when a packet needs more headroom. A nonsensical stacked
configuration can therefore incur an extra reallocation, but it cannot
publish an unbounded reservation to upper layers.
The Linux kernel CVE team has assigned CVE-2026-80978 to this issue.
Affected and fixed versions
===========================
Issue introduced in 3.11 with commit 1a37e412a0225fcba5587f24c0dfc7636efc8b69 and fixed in 6.12.109 with commit bc4e05ae66c9797a0972ac44326e69c5305e0020
Issue introduced in 3.11 with commit 1a37e412a0225fcba5587f24c0dfc7636efc8b69 and fixed in 6.18.50 with commit af0ee8f04bea22cdb331fa3509e17f81b48938ad
Issue introduced in 3.11 with commit 1a37e412a0225fcba5587f24c0dfc7636efc8b69 and fixed in 7.2.4 with commit 9144f2c53a04465a6878172b523f640313c5559e
Issue introduced in 3.11 with commit 1a37e412a0225fcba5587f24c0dfc7636efc8b69 and fixed in 7.3-rc1 with commit 6b222adeb9340306e2ff97127c76117abb9b3df8
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-2026-80978
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/ip_tunnels.h
net/ipv4/ip_tunnel.c
net/ipv6/ip6_gre.c
net/ipv6/ip6_tunnel.c
net/ipv6/sit.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/bc4e05ae66c9797a0972ac44326e69c5305e0020
https://git.kernel.org/stable/c/af0ee8f04bea22cdb331fa3509e17f81b48938ad
https://git.kernel.org/stable/c/9144f2c53a04465a6878172b523f640313c5559e
https://git.kernel.org/stable/c/6b222adeb9340306e2ff97127c76117abb9b3df8
reply other threads:[~2026-09-11 19:47 UTC|newest]
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