From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-64009: xfrm: Check for underflow in xfrm_state_mtu
Date: Sun, 19 Jul 2026 16:57:49 +0200 [thread overview]
Message-ID: <2026071908-CVE-2026-64009-4587@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
xfrm: Check for underflow in xfrm_state_mtu
Leo Lin reported OOB write issue in esp component:
xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned
modulo-2^32 space using an attacker-influenced "header_len + authsize +
net_adj" subtracted from a small "mtu" argument. A nobody user can
install an IPv4 ESP tunnel SA with a large authentication key
(XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc),
configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a
large value. When a single UDP datagram is then sent through the
tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and
esp_output() consumes it as a signed int via:
padto = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached))
esp.tfclen = padto - skb->len (assigned to int)
esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t
when passed to memset() inside esp_output_fill_trailer(), producing a
~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as
"Write of size 18446744073709551537 at addr ffff888...".
Check for underflow and return 1. This causes the sendmsg attempt to
fail with ENETUNREACH.
The Linux kernel CVE team has assigned CVE-2026-64009 to this issue.
Affected and fixed versions
===========================
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 5.10.259 with commit 8014f70c4e6e5ab101ae3860a614e65e988372e3
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 5.15.210 with commit 1021d2877b689a648b27815c854557a917122e93
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 6.1.176 with commit 2a41b1b31c61c52b972278ce1732a1443f5e89ed
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 6.6.143 with commit fccd685b32df5aaf6bad4381eeda216468e283f0
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 6.12.93 with commit 820e501be8aee4b365d218d83227b314309c5fda
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 6.18.35 with commit 82ac903e0b519849647657b8c48d21237ada06a2
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 7.0.12 with commit 3db50ceeacb52806d8fe86fb1dfe944df0b9f789
Issue introduced in 2.6.22 with commit c5c2523893747f88a83376abad310c8ad13f7197 and fixed in 7.1 with commit 742b04d0550b0ec89dcbc99537ec88653bd1ad90
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-2026-64009
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/xfrm/xfrm_state.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/8014f70c4e6e5ab101ae3860a614e65e988372e3
https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93
https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed
https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0
https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda
https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2
https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789
https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90
reply other threads:[~2026-07-19 15:03 UTC|newest]
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