[CVE-2026-68411][MODERATE REGULAR] wifi: mac80211_hwsim: clamp virtio RX length before skb_put [ Upstream

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

CVE: CVE-2026-68411
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: mac80211_hwsim: clamp virtio RX length before skb_put [ Upstream
Commit: 82c5a30a66e2a7337d99476c67d6fc1a99c4250e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82c5a30a66e2a7337d99476c67d6fc1a99c4250e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68411
Analysis date: Mon, 10 Aug 2026 20:16:48 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A malicious or compromised mac80211_hwsim virtio backend can report an oversized RX used-ring length, causing `skb_put()` to hit `skb_over_panic()` and crash the guest kernel, with impact limited to denial of service.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68411 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68411

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 REGULAR
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-2026-68411	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-617;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'mac80211_hwsim virtio RX handling can pass a device reported used ring length directly to skb_put() on a fixed size skb. A malicious or compromised virtio backend can report a length larger than the available skb tailroom, which triggers skb_over_panic() and crashes the guest kernel. For the CVSS the PR:L is used in the paranoid score because a compromised or delegated virtio backend process can provide the malicious virtqueue length without any privileges inside the guest. The issue is not directly network reachable and is not triggered by normal WiFi packet traffic. Impact is denial of service of the guest only, with no supported evidence of confidentiality impact, integrity impact, UAF, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)  SKIP CVE-2026-68411 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE DANGER VIRT SIMPLEFIX NETWORK SKB HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The malicious length is supplied by a virtio backend or device side component, not by ordinary guest WiFi packet traffic.
* Reliable kernel crash / strong DoS: +1. An oversized used-ring length reaches `skb_put()` and triggers `skb_over_panic()`, causing a guest kernel panic.

Paranoid additional signals:

* Constrained kernel buffer overwrite candidate: +1. The reported length drives skb metadata past the fixed receive skb boundary, but the demonstrated effect is the built-in skb bounds panic rather than attacker-controlled memory corruption.
* Availability impact realistic: +1. The impact is a reliable guest-wide kernel panic when a malicious or compromised backend can report the invalid length.

Negative / limiting factors:

* Rare or non-default exposure: -1 is defensible for conservative scoring because this is `mac80211_hwsim` over virtio, not a common production network receive path.
* No remote/network trigger: ordinary network packets do not directly reach this bug.
* No LPE signal: the patch and commit do not show UAF, object reuse, type confusion, arbitrary write, callback control, or privilege escalation.

Call-site confidence: high. The patch shows the direct call path: backend length -> `skb_put()` -> `hwsim_virtio_handle_cmd()`.

## 3. Reachability analysis

The bug is triggerable by a malicious, compromised, or delegated virtio backend that can report a used-ring RX length larger than the posted skb buffer. It is host-triggerable against the guest, but not remotely reachable through normal WiFi or IP packet traffic. A conforming virtio device should not report a length larger than the buffer, so realistic exploitation requires control over the backend or a faulty device model. Namespaces inside the guest do not materially lower the trigger requirements because the malformed length originates from the virtio device side, not from an unprivileged guest process.

## 4. Severity interpretation

This behaves like a strong DoS issue across a virtualization/device boundary, not like an Important-class memory corruption vulnerability. The theoretical boundary overrun is stopped by `skb_over_panic()`, and the commit explicitly says the clamped/truncated frame fails later length/header checks and is dropped. There is no supported evidence of confidentiality impact, integrity impact, privilege escalation, UAF, or attacker-controlled overwrite beyond the panic path. The issue should not be treated as ordinary network remote DoS, but it is still worth manual review because it is a guest-kernel panic controlled from the virtio backend side.

## 5. One-sentence report phrase

A malicious or compromised mac80211_hwsim virtio backend can report an oversized RX used-ring length, causing `skb_put()` to hit `skb_over_panic()` and crash the guest kernel, with impact limited to denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a virtualization boundary guest panic with a reliable DoS condition, but the evidence does not support privilege escalation or broader memory corruption.

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

Patch: wifi: mac80211_hwsim: clamp virtio RX length before skb_put [ Upstream
Commit: 82c5a30a66e2a7337d99476c67d6fc1a99c4250e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82c5a30a66e2a7337d99476c67d6fc1a99c4250e

Changed files:
  drivers/net/wireless/virtual/mac80211_hwsim.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=82c5a30a66e2a7337d99476c67d6fc1a99c4250e

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

The original Linux kernel CVE announcement for CVE-2026-68411 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68411

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).