[CVE-2026-74409][MODERATE 7.0] wifi: rtw89: add bounds check on firmware mac_id in link lookup [ Upstream

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

CVE: CVE-2026-74409
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: rtw89: add bounds check on firmware mac_id in link lookup [ Upstream
Commit: ad445de67359f24088d4305c05fbd7e34c4e35e3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ad445de67359f24088d4305c05fbd7e34c4e35e3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74409
Analysis date: Sat, 15 Aug 2026 08:42:30 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
The rtw89 driver failed to bounds-check a firmware supplied RX descriptor mac_id before indexing assoc_link_on_macid, allowing a firmware-mediated or adjacent WiFi influenced OOB pointer read that can plausibly crash the kernel and warrants manual review for downstream pointer misuse.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74409 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74409

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-2026-74409	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-129;CWE-125;*CWE-20;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'The rtw89 driver used the firmware supplied mac_id from RX descriptors as an index into assoc_link_on_macid without checking it against RTW89_MAX_MAC_ID_NUM. The descriptor field is 8 bit while the array has only 128 entries, so an out-of-range firmware value can cause an out-of-bounds read of a kernel pointer and may later lead to an invalid pointer dereference in the RX path. For the CVSS the PR:N is used for the paranoid score because an adjacent WiFi attacker would not need local code execution or credentials on the victim if the invalid mac_id can be induced through received traffic or firmware behavior. The issue is not Internet reachable, but it may be reachable from the local WiFi radio range on affected Realtek rtw89 devices. Impact is at least denial of service via driver or kernel crash. In worst case it may allow limited confidentiality or integrity impact because the bug reads a pointer outside the intended array and can feed that value into later driver logic.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74409 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE OOB SIMPLEFIX NETWORK LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	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: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The out-of-range `mac_id` comes from firmware-populated RX descriptors, not from a normal local syscall path.
* Memory corruption, weak/indirect corruption candidate: +1. The bug is an unchecked array index into `assoc_link_on_macid[]`, producing an OOB read of a kernel pointer-sized entry.
* Privileged kernel/device-management memory corruption path: +1. The affected code is in a trusted WiFi driver RX path and consumes firmware-provided metadata.
* Reliable kernel crash / strong DoS: +1. If the OOB pointer is later interpreted as a valid `rtw89_sta_link`, an invalid pointer dereference or driver crash is plausible.
* Corruption primitive highly constrained or metadata-only: -1. The patch shows an OOB read of a pointer array, but not an attacker-controlled write, reclaim primitive, callback overwrite, or arbitrary memory access.
* Availability impact realistic: +1. A malformed or unexpected firmware `mac_id` can plausibly crash the driver or kernel in the RX path.

Paranoid additional signal:

* Weak LPE concern: +1. A bogus object pointer returned from an OOB pointer-array lookup could theoretically feed later driver logic, but no concrete reclaim, write primitive, or type-confusion sink is shown.

Not counted:

* Remote reachable / network-triggerable +2 is not used. This is better modeled as firmware-mediated or adjacent WiFi influence, not Internet-reachable network parsing.
* Strong memory corruption +2 is not used. The patch does not show OOB write, UAF reclaim, double-free, or controlled overwrite.
* Confidentiality and integrity impact are not counted in the ActionableScore. They are only weakly plausible in a paranoid CVSS sense because there is no demonstrated read-back or write primitive.

## 3. Reachability analysis

The most realistic trigger is an affected Realtek `rtw89` WiFi device receiving RX descriptors where firmware reports a `mac_id` greater than or equal to `RTW89_MAX_MAC_ID_NUM`. A local user is not required if the condition can be induced by WiFi traffic or firmware behavior, but the attacker likely needs adjacent radio-range influence and the correct hardware and firmware path.

This is not broadly Internet-reachable. It is hardware and driver specific, but WiFi RX paths are externally influenced by nearby radio traffic. Namespaces and containers do not materially change reachability because the relevant input is below normal local namespace boundaries.

Call-site confidence: medium. The changed helper is clearly an RCU dereference helper for `assoc_link_on_macid[]`, but the full set of callers and downstream dereferences is not included in the patch input.

## 4. Severity interpretation

This is stronger than an ordinary low-risk validation fix because it prevents an OOB pointer-array lookup in a kernel WiFi RX path. Realistic impact is most likely DoS from invalid pointer use. Theoretical exploitation beyond DoS is not impossible, but the patch does not show a strong primitive such as an OOB write, UAF reclaim, refcount takeover, callback overwrite, or attacker-controlled object replacement.

Overall this should be treated as Actionable Moderate rather than auto-closed Moderate. It is not a Strong Important candidate on the supplied evidence.

## 5. One-sentence report phrase

The rtw89 driver failed to bounds-check a firmware supplied RX descriptor mac_id before indexing assoc_link_on_macid, allowing a firmware-mediated or adjacent WiFi influenced OOB pointer read that can plausibly crash the kernel and warrants manual review for downstream pointer misuse.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a kernel memory-safety boundary bug in a wireless RX path with firmware-controlled indexing, and the downstream use of the returned pointer should be reviewed before excluding confidentiality, integrity, or privilege-escalation relevance.

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UPSTREAM PATCH SUMMARY
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Patch: wifi: rtw89: add bounds check on firmware mac_id in link lookup [ Upstream
Commit: ad445de67359f24088d4305c05fbd7e34c4e35e3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ad445de67359f24088d4305c05fbd7e34c4e35e3

Changed files:
  drivers/net/wireless/realtek/rtw89/core.h

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=ad445de67359f24088d4305c05fbd7e34c4e35e3

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

The original Linux kernel CVE announcement for CVE-2026-74409 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74409

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

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: NO
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).