[CVE-2026-72451][MODERATE 7.0] xfrm: Fix xfrm state cache insertion race [ Upstream

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

CVE: CVE-2026-72451
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfrm: Fix xfrm state cache insertion race [ Upstream
Commit: 6dab4dec9a49121d079981ac913569f232c06b06
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6dab4dec9a49121d079981ac913569f232c06b06
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72451
Analysis date: Sat, 15 Aug 2026 22:02:43 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Strong Important candidate only if manual review confirms that the cached dead `xfrm_state` can survive into a freed or attacker-influenced reuse state.
Manual review required: YES

Summary:
A race in XFRM inbound state cache insertion can allow a dead `xfrm_state` to be cached after validation but before locking, creating a packet-path stale pointer or UAF candidate that can plausibly cause a kernel crash and requires manual review for deeper memory corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-72451 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72451

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: MODERATE 7.0
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-2026-72451	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A race in the XFRM inbound state cache can allow xfrm_input_state_lookup to add an xfrm_state to the per CPU input cache after the state has already become invalid. A later lookup may then observe a stale cached state on the network input path, which makes this a UAF candidate rather than a simple warning or resource leak. For the CVSS the PR:N is used for the paranoid score because the trigger can be packet driven when an XFRM or IPsec endpoint is reachable, although reliable exploitation still depends on a narrow race with state deletion or expiration. AC:H is used because the attacker must hit a timing window and the target must have a relevant XFRM state configuration. Impact is at least remote denial of service via kernel crash, and in the paranoid interpretation it may allow confidentiality or integrity impact due to stale pointer or UAF style memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	LOCK DANGER SIMPLEFIX RACE HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Strong Important candidate only if manual review confirms that the cached dead `xfrm_state` can survive into a freed or attacker-influenced reuse state.

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  `xfrm_input_state_lookup()` is on the XFRM/IPsec input path, so packet traffic to a configured IPsec/XFRM endpoint can drive the lookup path.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch prevents insertion of a dead `xfrm_state` into the per-CPU input cache. This is a stale object / UAF candidate, but the patch does not show controlled reclaim, overwrite, callback control, or type confusion.

* Real lifetime corruption: +1
  The bug is a race between state validity checking and state destruction, allowing a dying object to be cached.

* Reliable kernel crash / strong DoS: +1
  A later lookup through a stale cached state can plausibly produce a kernel crash or invalid dereference.

* Hard or unreliable race / special timing required: -1
  Exploitation requires hitting a race between inbound lookup/cache insertion and XFRM state invalidation or destruction.

Paranoid additional signal:

* Common networking / packet-processing path: +1
  Although IPsec/XFRM must be configured, this is still a kernel network input path and should not be treated as an obscure local-only control-plane bug.

Race-UAF downgrade applied:

* Because the patch shows a stale/dead object cache insertion race but does not demonstrate attacker-controlled reclaim, write-after-free, callback dispatch, refcount takeover, or type confusion, the conservative score is capped at 4 and paranoid score at 5.

## 3. Reachability analysis

A remote peer or attacker who can send packets to a configured XFRM/IPsec endpoint may exercise the affected input lookup path. Reliable triggering also requires a concurrent state lifecycle event such as deletion, expiration, rekey, or teardown of the relevant XFRM state. Local `CAP_NET_ADMIN` is normally required to configure or delete XFRM state directly, but the packet-driven side of the race can be remote once the endpoint and state exist. Network namespaces matter because XFRM state is per-netns, but an unprivileged container normally cannot manipulate host XFRM state without delegated capabilities. The path is common in IPsec deployments but not active by default on systems that do not use XFRM/IPsec.

Call-site confidence: medium. The patch includes the affected lookup and cache insertion code, but not the full state teardown and later cache-consumer paths.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a network input path lifetime race involving a cached kernel object. The realistic demonstrated impact is remote or adjacent-network DoS under IPsec/XFRM configuration and timing constraints. The theoretical risk is UAF-style memory corruption if a dead cached `xfrm_state` can later be freed and reused before another lookup, but the supplied patch does not demonstrate a practical privilege-escalation primitive. Therefore the conservative result is borderline/manual-review, while the paranoid result is Actionable Moderate.

## 5. One-sentence report phrase

A race in XFRM inbound state cache insertion can allow a dead `xfrm_state` to be cached after validation but before locking, creating a packet-path stale pointer or UAF candidate that can plausibly cause a kernel crash and requires manual review for deeper memory corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable XFRM/IPsec input-path race involving object lifetime and a stale cached kernel state object. Even though the patch does not prove LPE or controlled reuse, the combination of network exposure, ZDI reporting, and UAF-like lifetime semantics should not be auto-closed.

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

Patch: xfrm: Fix xfrm state cache insertion race [ Upstream
Commit: 6dab4dec9a49121d079981ac913569f232c06b06
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6dab4dec9a49121d079981ac913569f232c06b06

Changed files:
  net/xfrm/xfrm_state.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=6dab4dec9a49121d079981ac913569f232c06b06

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

The original Linux kernel CVE announcement for CVE-2026-72451 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72451

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 4
  Paranoid ActionableScore: 5

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).