CVE-2026-80844: xfrm: ah6: validate routing header segments_left

CVE-2026-80844: xfrm: ah6: validate routing header segments_left

[Greg Kroah-Hartman]

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

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

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

xfrm: ah6: validate routing header segments_left

AH6 rearranges routing-header addresses before computing or verifying the
ICV. ipv6_rearrange_rthdr() assumes that segments_left is not larger than
the number of addresses described by the routing header's hdrlen field.

That assumption does not hold for raw IPv6 HDRINCL packets. A packet with
hdrlen equal to 2 describes one address, but can carry an arbitrary
segments_left value. With segments_left equal to 255, the function moves
its address pointer 4,064 bytes backwards and passes a 4,064-byte length to
memmove(), resulting in an out-of-bounds access.

Validate the invariant locally before modifying the routing header or
performing any address-pointer arithmetic, and propagate malformed-header
errors to the existing AH6 input and output error paths.

The Linux kernel CVE team has assigned CVE-2026-80844 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.10.269 with commit 2dc650956e4e163b879b3fb1027f9557abc5c985
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 5.15.220 with commit 48b0e36cf54358276ee7aa897034c973097d2bc9
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.187 with commit 1b7e066eabcc7d6d8f476c34739b45932f2f4c31
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.156 with commit f00df8500e5a36ba70d336fd34bd2152ea074e5f
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.108 with commit 1516e31ac458a738be485620579d8f7fb2700fcb
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.49 with commit 6733ae71268a27d598cfb3f3339a3c950b9b656d
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.13 with commit 0bf11081ad3753938a2b48723ce6298dbac743a1
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2.3 with commit 46640c814f25f096b0b0045ca50e1b7030cd8a30
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.3-rc1 with commit 7bad4bda74dc4713f398d3b7624ff05478e3a568

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-2026-80844
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/ipv6/ah6.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/2dc650956e4e163b879b3fb1027f9557abc5c985
	https://git.kernel.org/stable/c/48b0e36cf54358276ee7aa897034c973097d2bc9
	https://git.kernel.org/stable/c/1b7e066eabcc7d6d8f476c34739b45932f2f4c31
	https://git.kernel.org/stable/c/f00df8500e5a36ba70d336fd34bd2152ea074e5f
	https://git.kernel.org/stable/c/1516e31ac458a738be485620579d8f7fb2700fcb
	https://git.kernel.org/stable/c/6733ae71268a27d598cfb3f3339a3c950b9b656d
	https://git.kernel.org/stable/c/0bf11081ad3753938a2b48723ce6298dbac743a1
	https://git.kernel.org/stable/c/46640c814f25f096b0b0045ca50e1b7030cd8a30
	https://git.kernel.org/stable/c/7bad4bda74dc4713f398d3b7624ff05478e3a568