[CVE-2026-72407][MODERATE 7.0] geneve: validate inner network offset in geneve_gro_complete() [ Upstream

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

CVE: CVE-2026-72407
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: geneve: validate inner network offset in geneve_gro_complete() [ Upstream
Commit: e2087447f562692ff0cd08a0554d8d4ad083aa5c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e2087447f562692ff0cd08a0554d8d4ad083aa5c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72407
Analysis date: Sun, 16 Aug 2026 08:22:14 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Geneve GRO completion may recompute an inner packet offset that is inconsistent with the offset validated during receive, allowing crafted Geneve traffic to drive completion past the validated inner network header and potentially crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-72407 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72407

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.

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

CVE-2026-72407	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-125;CWE-362;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Geneve GRO completion can recompute the inner dispatch offset independently from the offset validated earlier by geneve_gro_receive(). If the GRO hint state changes between receive and complete, or if the option bytes used by completion differ from the bytes parsed during receive, geneve_gro_complete() may dispatch past the validated inner network header. A remote peer can potentially trigger this through crafted Geneve traffic when the Geneve endpoint and GRO hint path are reachable, although practical exposure is usually limited to overlay or data center networks. For the CVSS the PR:N is used because no local account on the victim is needed when the tunnel endpoint accepts attacker controlled packets. Impact is at least denial of service via invalid packet completion and possible kernel crash. For the paranoid score, limited confidentiality or integrity impact is kept for manual-review sensitivity because this is an out-of-bounds parser offset condition, but no strong write primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-72407 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: fd0dd796576e1a560e1441e665810129f0a82be0 YES  NO NO unknown 	MAYBE	WRITE OOB NETWORK SKB KPANIC PACKET  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  Geneve packets can reach this path when a Geneve endpoint is configured and accepts attacker-controlled traffic.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is an invalid parser or completion offset condition. `geneve_gro_complete()` can dispatch past the inner network header previously validated by `geneve_gro_receive()`. This supports an OOB or invalid skb parsing concern, but not a proven OOB write or UAF.

* Memory layout invariant restoration: +1
  The patch restores consistency between `gh_len`, computed completion offset, and `NAPI_GRO_CB(skb)->inner_network_offset` in networking buffer parsing.

* Reliable kernel crash / strong DoS: +1
  Dispatching GRO completion past the validated inner header can plausibly crash or destabilize packet processing.

* Hard or unreliable race / special timing required: -1
  One described trigger depends on `gro_hint` changing under concurrent `geneve_quiesce()` / `geneve_unquiesce()`, or on completion re-reading different option bytes than receive parsed.

Conservative total: 4

Paranoid additional signal:

* Common networking packet-processing path: +1
  Although Geneve is deployment-specific, this is still a network receive/GRO completion path for a tunnel endpoint and deserves manual network-parser scrutiny when enabled.

Paranoid total: 5

## 3. Reachability analysis

A remote peer can potentially trigger the issue by sending crafted Geneve traffic to a configured Geneve tunnel endpoint. No local account on the victim is required if the endpoint accepts attacker-controlled packets, so practical CVSS PR is `PR:N`.

The path is not universally default-exposed. Geneve is typically used in overlay, virtualization, cloud, or data-center networks, not as a public Internet service. Exploitation therefore usually requires access to the overlay or trusted internal network where Geneve is deployed.

Namespaces and containers mainly affect who can configure Geneve devices, but the packet-trigger side is remote once the endpoint exists. The main reliability limiter is the GRO hint mismatch or race-like condition, so the trigger is not as straightforward as a normal protocol NULL dereference.

Call-site confidence: medium. The provided patch shows the vulnerable completion path and the validation check, but not all GRO call sites or exact crash behavior.

## 4. Severity interpretation

This is more than an ordinary low-risk Moderate because it is a network-triggerable packet parser offset bug in a kernel tunnel GRO path. Conservative handling is Borderline / manual review recommended with score 4.

The paranoid score is Actionable Moderate with score 5 because network reachability plus an out-of-bounds completion condition can be underestimated during early triage. However, the patch does not show a strong write primitive, UAF, type confusion, callback control, or attacker-controlled object replacement. Realistic demonstrated impact is DoS. Limited confidentiality or integrity concern remains theoretical and should not be treated as proven privilege escalation.

## 5. One-sentence report phrase

Geneve GRO completion may recompute an inner packet offset that is inconsistent with the offset validated during receive, allowing crafted Geneve traffic to drive completion past the validated inner network header and potentially crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: network reachable when Geneve is deployed, affects packet parsing in the GRO completion path, and has a plausible OOB parser-offset condition, but no demonstrated strong memory corruption or LPE primitive.

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

Patch: geneve: validate inner network offset in geneve_gro_complete() [ Upstream
Commit: e2087447f562692ff0cd08a0554d8d4ad083aa5c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e2087447f562692ff0cd08a0554d8d4ad083aa5c

Changed files:
  drivers/net/geneve.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=e2087447f562692ff0cd08a0554d8d4ad083aa5c

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

The original Linux kernel CVE announcement for CVE-2026-72407 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72407

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:L/I:L/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: 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).