[CVE-2026-80844][IMPORTANT] xfrm: ah6: validate routing header segments_left

[CVE-2026-80844][IMPORTANT] xfrm: ah6: validate routing header segments_left

[AL-KERNEL]

CVE: CVE-2026-80844
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: xfrm: ah6: validate routing header segments_left
Commit: 2dc650956e4e163b879b3fb1027f9557abc5c985
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc650956e4e163b879b3fb1027f9557abc5c985
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80844
Analysis date: Fri, 04 Sep 2026 14:06:07 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
AH6 can perform an attacker-influenced out-of-bounds memmove while rearranging IPv6 routing-header addresses for AH ICV processing, allowing a local raw IPv6 HDRINCL packet path to crash the kernel and requiring manual review for possible memory-corruption impact.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80844 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80844

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: IMPORTANT
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80844	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-80844 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-20;*CWE-787;CWE-125;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'AH6 can perform out of bounds memory access while rearranging an IPv6 routing header before AH ICV calculation or verification. The bug occurs because ipv6_rearrange_rthdr assumes that segments_left is not larger than the number of addresses encoded by hdrlen, but raw IPv6 HDRINCL packets can violate this invariant. A crafted local raw IPv6 packet with a small hdrlen and a large segments_left value can make the address pointer move backwards and can pass a large length to memmove, leading to kernel memory access outside the expected routing header buffer. For the CVSS the PR:L is used because reliable triggering requires a local process able to create such raw IPv6 traffic and usually depends on local AH6 XFRM use, not merely remote packet delivery. The issue is not considered directly network reachable from the patch context. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to an out of bounds memory access primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)  SKIP CVE-2026-80844 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE OOB SIMPLEFIX ERRORPATH NETWORK LINUS IPV6 KPANIC PACKET 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the conservative score.
No floor or cap changed the paranoid score.

## 2. Signal breakdown

Conservative signals:

* +2: Strong corruption primitive. The patch establishes an out-of-bounds `memmove()` caused by an invalid relationship between `segments_left` and `hdrlen` in an IPv6 routing header.
* +1: Reliable kernel crash / strong DoS. A 4064-byte out-of-bounds access in kernel packet processing is a realistic kernel crash condition.
* +1: Memory layout invariant restoration. The fix restores the required invariant between routing-header address count and `segments_left` before pointer arithmetic and copy length calculation.
* +1: Attacker-controlled structured input. Raw IPv6 HDRINCL packets can carry attacker-selected `hdrlen` and `segments_left`, directly influencing the invalid pointer arithmetic and copy size.

Paranoid additional signal:

* +1: Weak LPE / integrity concern. The primitive is not a NULL dereference or passive invalid read. It is an attacker-influenced out-of-bounds memory operation via `memmove()`, so post-crash exploitation leverage cannot be excluded without manual review.

Important non-awarded signals:

* RealUAF not awarded. No use-after-free or stale lifetime object is established.
* Concrete repeated release/refcount not awarded. No repeated put/free/refcount mutation exists.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality impact not awarded. No concrete disclosure path is shown.
* Direct remote reachability not awarded. The described violating path is locally generated raw IPv6 HDRINCL traffic.
* Extra availability point not awarded. The crash/DoS consequence is already counted once.
* NamespaceScopedPrivilege=UNKNOWN because the input does not prove that the complete AH6/XFRM trigger chain is reachable inside attacker-created namespaces.

## 3. Reachability analysis

The clearest trigger is a local process generating raw IPv6 HDRINCL packets with malformed routing-header state. Creating raw IPv6 packets normally requires `CAP_NET_RAW`, and reaching AH6 processing may also depend on AH6/XFRM configuration or an existing IPsec AH setup.

Host-admin-equivalent privilege is not positively established for the complete trigger, so `HostAdminRequired=UNKNOWN`, not YES. However, below-host-admin reachability is also not fully proven because the complete AH6 path may depend on prior XFRM/AH policy or configuration.

The issue is not scored as directly network-triggerable. The commit specifically identifies raw locally generated packets as the path that violates the invariant. Incoming packet paths may have different validation before AH6 reaches this function.

No special physical hardware is required. No hard race is involved. The trigger is a malformed packet construction path, not a timing-dependent lifetime race.

## 4. Primitive and severity interpretation

The exact primitive is an attacker-influenced out-of-bounds memory access in `ipv6_rearrange_rthdr()`. The invalid `segments_left` value causes address-pointer arithmetic to move outside the routing-header address array and causes a large `memmove()` length.

This is not a fixed stale-storage UAF and not cleanup-only behavior. It is active packet-buffer processing with an invalid copy range.

Primitive class is `CLASS_A` because a concrete out-of-bounds memory operation is directly established. The demonstrated consequence is kernel crash / DoS. The speculative but technically defensible consequence is kernel memory corruption with possible integrity impact or privilege-escalation relevance, depending on exact skb layout and copy direction.

`ImportantCandidate=YES` because the primitive is stronger than ordinary DoS-only validation failure.
`AutoDowngradeAllowed=NO` because automatically closing this as ordinary Moderate would discard an established kernel OOB `memmove()` corruption primitive.

Operationally, this should be treated as Actionable Moderate at minimum and a Strong Important candidate requiring manual analysis of the exact AH6 output/input call paths, skb layout, and privilege boundary.

## 5. One-sentence report phrase

AH6 can perform an attacker-influenced out-of-bounds memmove while rearranging IPv6 routing-header addresses for AH ICV processing, allowing a local raw IPv6 HDRINCL packet path to crash the kernel and requiring manual review for possible memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a concrete out-of-bounds `memmove()` in kernel networking code with attacker-controlled header fields, and the exploitability beyond DoS depends on memory-layout and call-path details not resolved by the patch alone.

## 7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: xfrm: ah6: validate routing header segments_left
Commit: 2dc650956e4e163b879b3fb1027f9557abc5c985
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc650956e4e163b879b3fb1027f9557abc5c985

Commit description:

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.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Assisted-by: avom-custom-harness:gpt-5.5-qwen3.6-mod-mix
Signed-off-by: Asim Viladi Oglu Manizada <manizada@pm.me>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/ah6.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dc650956e4e163b879b3fb1027f9557abc5c985

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80844 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80844

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 5
  Paranoid ActionableScore: 6

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).