[CVE-2026-98829][MODERATE 7.0] wifi: mac80211: drop oversized fragments to avoid extra_len overflow [ Upstream

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

CVE: CVE-2026-98829
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: wifi: mac80211: drop oversized fragments to avoid extra_len overflow [ Upstream
Commit: 9338b2dea74cb0fc80a4c958b68e687610ba2261
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9338b2dea74cb0fc80a4c958b68e687610ba2261
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98829
Analysis date: Sat, 24 Oct 2026 08:42:23 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An adjacent malicious Wi-Fi sender can overflow the mac80211 fragment-length accumulator and trigger `skb_over_panic()`, causing a kernel DoS without a demonstrated OOB write.

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

The original Linux kernel CVE announcement for CVE-2026-98829 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98829

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-2026-98829	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98829 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-190;CWE-131;**CWE-400;BEST CVSS score: '6.5';DESCR 'A u16 overflow in mac80211 fragment reassembly can truncate entry extra_len after a malicious peer supplies a sequence of oversized fragments whose accumulated payload exceeds U16_MAX. The truncated value can cause insufficient skb tailroom to be reserved before the complete queued payload is appended, causing skb_put to call skb_over_panic and crash the kernel in softirq context. For the CVSS the PR:N value is used because an adjacent malicious WiFi peer or rogue access point does not need privileges on the target host. AV:A reflects the required local radio or wireless network proximity. The fragment sequence is unusual but directly attacker controlled, so AC:L is defensible. The demonstrated primitive is a kernel panic rather than an OOB write because skb_put detects the insufficient tailroom and terminates through skb_over_panic before the copy proceeds beyond the buffer. Confidentiality and integrity therefore remain N while availability is H. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 6.5 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage IMPORTANT to MODERATE_KPANIC because the ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5. The independent weaker Aegis shadow evaluated CVSS 6.5 and ActionableScore 4 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	REMOTE DANGER SKB KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 4; no floor or cap applied.
* Raw paranoid score: 4.
* Paranoid score: 4; no additional technically supported primitive.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 clearly network-reachable: a nearby malicious Wi-Fi peer or rogue AP can supply the fragment sequence without target-host privileges.
* +1 common packet-processing path: mac80211 receive defragmentation processes attacker-supplied wireless frames.
* +1 reliable kernel crash/strong DoS: wrapped `extra_len` under-reserves tailroom, and `skb_put()` invokes `skb_over_panic()` in softirq context.
* No extra Availability point: it would duplicate the same panic.
* No OOB-write point: the supplied path shows the `skb_put()` bounds check panicking before `skb_put_data()` copies beyond the allocation.
* No C/I, arbitrary-write, UAF, disclosure, authorization-bypass, or protected-resource signal.
* B5-R does not apply: there is neither a confirmed heap OOB write nor retry-accumulated indexing followed by corrupted-state consumption.
* No timing or privilege penalty: this is a directly attacker-shaped fragment sequence, not a demonstrated hard race or host-admin operation.

3. Reachability analysis

The supported attacker is an adjacent wireless peer or rogue AP controlling fragment sizes and ordering. No local account, host UID 0, capability, namespace privilege, or prior privileged host configuration is required. Wireless proximity and a functioning mac80211 interface are required, but ordinary Wi-Fi hardware is not evidence of rare physical-only hardware. The sequence is unusual but directly repeatable by the sender.

4. Primitive and severity reading

The exact defect is a `u16` arithmetic wrap causing insufficient skb tailroom reservation. The later append is guarded by `skb_put()` and therefore produces a panic rather than a confirmed heap overwrite. This is CLASS_C crash/DoS behavior, not NEW52/B5-R corruption. Stronger memory-corruption or integrity effects are unsupported. ImportantCandidate is NO and auto-downgrade is allowed because no non-crash primitive or unresolved trust-boundary corruption chain remains.

5. One-sentence report phrase

An adjacent malicious Wi-Fi sender can overflow the mac80211 fragment-length accumulator and trigger `skb_over_panic()`, causing a kernel DoS without a demonstrated OOB write.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm affected-driver exposure and whether product panic/oops policy makes the softirq fault host-fatal.

7. Call-site confidence

Call-site confidence: high

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

Patch: wifi: mac80211: drop oversized fragments to avoid extra_len overflow [ Upstream
Commit: 9338b2dea74cb0fc80a4c958b68e687610ba2261
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9338b2dea74cb0fc80a4c958b68e687610ba2261

Changed files:
  net/mac80211/drop.h
  net/mac80211/rx.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=9338b2dea74cb0fc80a4c958b68e687610ba2261

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

The original Linux kernel CVE announcement for CVE-2026-98829 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98829

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: Not available
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: unknown
  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: 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).