[CVE-2026-72408][MODERATE 7.0] geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint [ Upstream

[CVE-2026-72408][MODERATE 7.0] geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72408
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint [ Upstream
Commit: 49c2e7c0a69999a75ef5eaebe1559a20d0b3c15a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49c2e7c0a69999a75ef5eaebe1559a20d0b3c15a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72408
Analysis date: Sat, 15 Aug 2026 23:20:50 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A network-reachable Geneve GRO completion bug allows attacker-supplied GRO hint data to desynchronize header offset handling and trigger an skb head out-of-bounds read, causing a kernel crash and requiring manual review due to remote packet-path exposure.

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

The original Linux kernel CVE announcement for CVE-2026-72408 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72408

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-2026-72408	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'A remote out-of-bounds read in the Geneve GRO complete path can occur because geneve_gro_complete() honored an attacker supplied GRO hint even when the Geneve socket did not enable GRO hints. The receive path treats such packets as plain ETH_P_TEB, but the complete path can inflate gh_len and redirect the inner protocol dispatch so the next gro_complete handler reads from an offset that was not pulled or validated. For the CVSS the PR:N because an attacker only needs network reachability to a vulnerable Geneve tunnel endpoint and does not need local code execution on the victim. The issue is network reachable over Geneve UDP when the tunnel endpoint is exposed to the attacker, although Geneve is typically deployed inside overlay or data center networks rather than the public Internet. Impact is at least denial of service via kernel crash. For the paranoid score, limited confidentiality and integrity impact is kept for manual review sensitivity because this is a network reachable skb out-of-bounds read, but the patch context does not show a write primitive or reliable privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-72408 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: fd0dd796576e1a560e1441e665810129f0a82be0 YES  NO NO unknown 	MAYBE	READ KASAN OOB NETWORK SKB LINUS IPV6 KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **6**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* **Remote reachable / network-triggerable: +2**
  A crafted Geneve packet can reach `geneve_gro_complete()` over the network when a vulnerable Geneve tunnel endpoint is exposed.

* **Reliable kernel crash / strong DoS: +1**
  The report shows a concrete KASAN `slab-out-of-bounds` read in `ipv6_gro_complete()` from the GRO completion path. This is a realistic kernel crash / DoS condition.

* **Memory layout invariant restoration: +1**
  The patch restores consistency between the receive and complete paths for `gro_hint`, `gh_len`, protocol dispatch, and the inner header offset. The bug is specifically caused by `geneve_gro_receive()` and `geneve_gro_complete()` disagreeing about whether the hint is valid.

* **Common networking packet-processing path: +1**
  The bug is in GRO completion for a UDP tunnel protocol and is reached from packet receive/offload processing.

* **Availability impact realistic: +1**
  The failure is an easy network-triggered crash once the vulnerable tunnel endpoint is reachable.

Subtracting signals:

* **Configuration / exposure limitation: -1**
  Geneve tunnel endpoints are commonly used in overlay or data-center networks, but they are not normally exposed to the public Internet and require a configured Geneve tunnel.

Paranoid-only signal:

* **Confidentiality impact plausible: +1**
  The primitive is an out-of-bounds read from skb head memory. No direct disclosure path is shown, so this is not used for the conservative score, but it is defensible for manual-review sensitivity.

Not awarded:

* **Generic strong memory corruption: +0**
  The patch shows an OOB read, not UAF, OOB write, double-free, controlled overwrite, or object replacement.

* **Privilege escalation plausible: +0**
  No reclaim, write primitive, callback control, type confusion, or refcount takeover is shown.

* **Integrity impact plausible: +0 conservative**
  Protocol dispatch is redirected, but the demonstrated primitive is a read-side OOB crash, not a write or persistent state corruption.

## 3. Reachability analysis

An attacker can trigger this if they can send crafted Geneve traffic to a vulnerable Geneve tunnel endpoint. No local account on the victim is required, so the practical attacker privilege is network reachability rather than local privileges. Namespaces and containers matter mainly for deployment because Geneve is often used in virtualized or overlay networking, but the vulnerable endpoint itself is in the host kernel packet-processing path.

The path is not universally default-enabled because Geneve tunnels must be configured. However, in environments that use Geneve overlays, the affected packet path is realistic and reachable by network peers inside the overlay or data-center network.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is network-triggerable and has a concrete OOB read crash in a kernel packet path. It is not a strong Important memory-corruption candidate because the shown primitive is read-only OOB access with no demonstrated disclosure, write, UAF, reclaim, or privilege-escalation path.

Conservatively, this is **Actionable Moderate** and should not be auto-closed. Paranoid triage can treat it as a lower-end **Important candidate** for manual review because network-reachable skb parsing bugs are historically easy to underestimate.

## 5. One-sentence report phrase

A network-reachable Geneve GRO completion bug allows attacker-supplied GRO hint data to desynchronize header offset handling and trigger an skb head out-of-bounds read, causing a kernel crash and requiring manual review due to remote packet-path exposure.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the bug is network-reachable, has a concrete skb out-of-bounds read in GRO packet processing, and causes a reliable kernel crash. No strong LPE primitive is shown, but the combination of remote reachability and kernel OOB access should be reviewed manually.

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

Patch: geneve: gate GRO hint in geneve_gro_complete() on gs->gro_hint [ Upstream
Commit: 49c2e7c0a69999a75ef5eaebe1559a20d0b3c15a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=49c2e7c0a69999a75ef5eaebe1559a20d0b3c15a

Changed files:
  net/ipv6/ip6_offload.c
  drivers/net/geneve.c
  net/ipv4/udp_offload.c
  net/ipv4/af_inet.c
  net/core/gro.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=49c2e7c0a69999a75ef5eaebe1559a20d0b3c15a

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

The original Linux kernel CVE announcement for CVE-2026-72408 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72408

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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 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).