[CVE-2026-80845][LOW] xfrm: avoid lock inversion in nat keepalive work

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-80845
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xfrm: avoid lock inversion in nat keepalive work
Commit: ea09210462316e5235a25eccb11ad0708d86615e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ea09210462316e5235a25eccb11ad0708d86615e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80845
Analysis date: Fri, 04 Sep 2026 16:19:29 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80845 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80845

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: LOW
Manual review required: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-80845	LOW	https://www.kernelcve.org/list/?q=CVE-2026-80845 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-833;CWE-667;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An AB BA locking issue in xfrm NAT keepalive work can deadlock when nat_keepalive_work walks the XFRM state table while holding xfrm_state_lock and then tries to acquire the per state lock, while SA deletion can take the same locks in the opposite order. A local actor who can create or delete IPsec XFRM state and trigger NAT keepalive processing may cause the worker and delete path to block each other, leading to denial of service for XFRM/IPsec control plane operations and possible network degradation. For the CVSS the PR:L is used for the paranoid score because delegated CAP_NET_ADMIN, container root, or a reduced capability network service may be able to manage XFRM state without full host root. The issue is not directly network reachable, because packet traffic alone is not enough for reliable triggering without local control of XFRM state lifecycle. Impact is availability only because the patch context shows a lock inversion and deadlock, not memory corruption or an information disclosure primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-80845 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	LOCK DEADLOCK DANGER INIT NOMEMCHK RACE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

Positive signals:

* +1 Concrete AB-BA deadlock primitive. The patch and commit establish a real lock inversion between nat_keepalive_work() and xfrm_state_delete() / __xfrm_state_delete().
* +1 Denial of service impact. The deadlock can block XFRM/IPsec state handling and related control-plane operations.

Negative or non-awarded signals:

* 0 Remote reachability not awarded. Packet traffic alone is not enough to reach the vulnerable lock ordering without control of XFRM SA lifecycle.
* 0 Local unprivileged trigger not awarded. The complete trigger appears to require XFRM/IPsec state management privileges.
* 0 Host-admin penalty not applied. Host-admin-equivalent privilege is not positively established because XFRM operations may be namespace or delegated capability scoped depending on deployment.
* 0 Race/timing penalty not applied. The bug involves a race, but the evidence does not prove a one-shot or externally uncontrollable timing window.
* 0 Memory corruption not awarded. The patch shows lock inversion and deadlock, not UAF, OOB, double free, refcount corruption, arbitrary write, or disclosure.
* 0 C/I impact not awarded. There is no confidentiality or integrity primitive.
* 0 Extra availability point not awarded. The availability impact is the same deadlock/DoS consequence already counted.
* No repeated release/refcount operation exists. No first release can end lifetime, no exact dangling reference survives, and no second lifetime/refcount mutation is shown. FLOOR 5 does not apply.

3. Reachability analysis

The likely trigger requires a local actor or management component able to create, delete, or otherwise manipulate XFRM/IPsec Security Associations with NAT keepalive enabled while the NAT keepalive worker is running. In normal Linux deployments, XFRM state management is privilege-gated, typically through CAP_NET_ADMIN over the relevant network namespace or host network configuration.

HostAdminRequired is UNKNOWN because the supplied evidence does not prove that the required CAP_NET_ADMIN must be host/init namespace CAP_NET_ADMIN. NamespaceScopedPrivilege is UNKNOWN because the patch does not establish that the full chain, including creating the relevant XFRM state, enabling NAT keepalive behavior, deleting the SA, and racing the worker, is completely reachable inside an attacker-created namespace.

There is no direct network trigger. Remote packets may influence IPsec state activity in a deployed system, but the vulnerable condition is control-plane lock ordering during NAT keepalive work and SA deletion, not ordinary packet processing alone. No special hardware, firmware, boot option, or rare physical device prerequisite is established. The race is real but not enough by itself to apply an additional hard-timing penalty.

4. Primitive and severity interpretation

The exact primitive is a lock inversion: nat_keepalive_work() walks XFRM state while xfrm_state_lock is held and then acquires x->lock, while the delete path can acquire the same locks in the opposite order. This is Class C because the demonstrated result is deadlock/DoS without a useful kernel corruption or security-boundary primitive.

There is no active structured UAF, no fixed stale storage UAF, and no cleanup/destructor stale dereference. There is also no concrete repeated release/refcount mutation. The demonstrated consequence is availability loss affecting XFRM/IPsec state operations and potentially network behavior relying on those states. Stronger consequences such as privilege escalation, kernel memory corruption, or information disclosure are speculative and not supported by the patch.

ImportantCandidate is NO because the issue is a grounded DoS-only locking bug with no unresolved memory-corruption or authorization-boundary primitive. AutoDowngradeAllowed is YES because automatic downgrade would not discard a concrete UAF, repeated lifetime mutation, controlled corruption, COW violation, or security-boundary bypass. Operational severity is Ordinary Moderate.

5. One-sentence report phrase

An AB-BA lock inversion in XFRM NAT keepalive processing can deadlock when NAT keepalive work races with SA deletion, causing denial of service for XFRM/IPsec control-plane operations without evidence of memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a lock inversion and DoS condition only, with no UAF, repeated refcount mutation, disclosure, integrity impact, or security-boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: xfrm: avoid lock inversion in nat keepalive work
Commit: ea09210462316e5235a25eccb11ad0708d86615e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ea09210462316e5235a25eccb11ad0708d86615e

Commit description:

nat_keepalive_work() walks the state table while xfrm_state_walk()
holds net->xfrm.xfrm_state_lock. Its callback then acquires x->lock,
which conflicts with the delete path taking the same locks in reverse
order via xfrm_state_delete() and __xfrm_state_delete(). This creates
an AB-BA deadlock that is reported by lockdep when a NAT keepalive
worker races with SA deletion.

Fix this by splitting the keepalive walk into two phases. First,
collect the candidate states while the walk holds xfrm_state_lock and
take a reference on each state. Then, after the walk completes, process
each collected state and acquire x->lock without nesting it under
xfrm_state_lock.

Fixes: f531d13 ("xfrm: support sending NAT keepalives in ESP in UDP states")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Zihan Xi <xizh2024@lzu.edu.cn>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/xfrm/xfrm_nat_keepalive.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=ea09210462316e5235a25eccb11ad0708d86615e

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

The original Linux kernel CVE announcement for CVE-2026-80845 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80845

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:H/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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).