[CVE-2026-64255][MODERATE 7.0] wifi: iwlwifi: mld: validate sta_mask before ffs() in BA session handlers

[CVE-2026-64255][MODERATE 7.0] wifi: iwlwifi: mld: validate sta_mask before ffs() in BA session handlers

[AL-KERNEL]

CVE: CVE-2026-64255
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: wifi: iwlwifi: mld: validate sta_mask before ffs() in BA session handlers
Commit: 1de92789ce31e46fa7e7d8e89c90b19cdb1c103b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1de92789ce31e46fa7e7d8e89c90b19cdb1c103b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64255
Analysis date: Fri, 24 Jul 2026 12:51:59 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A zero sta_mask in iwlwifi MLD BA session handlers can make ffs() produce an invalid station id, causing an out-of-bounds access on fw_id_to_link_sta and a likely driver or kernel crash, with adjacent Wi-Fi or firmware-mediated triggering conditions requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64255 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64255

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-2026-64255	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-125;CWE-129;*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 'An out-of-bounds access in the iwlwifi MLD BA session handling path can occur because ffs(ba_data sta_mask) - 1 is used without first validating that sta_mask is nonzero. If sta_mask is zero, ffs() returns 0 and the derived station id becomes invalid, leading to an out-of-bounds access on fw_id_to_link_sta and a possible invalid link_sta dereference. For the CVSS the PR:N because an adjacent wireless attacker may be able to influence BA session handling without a local account on the target system. The issue is not reachable over the public Internet as a normal IP network bug and is best treated as adjacent Wi-Fi exposure. Impact is at least denial of service via driver crash or kernel warning path, with limited confidentiality or integrity impact kept only for paranoid manual-review sensitivity due to the OOB pointer access pattern.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB SIMPLEFIX NETWORK KPANIC 	NO	NO	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 affected state is in an iwlwifi BA session path and may be influenced by wireless firmware or adjacent Wi-Fi protocol state, but this is not ordinary Internet remote reachability.

* Memory corruption, weak/indirect corruption candidate: +1
  A zero `sta_mask` makes `ffs()` return 0, producing an invalid station id and an out-of-bounds access on `fw_id_to_link_sta[]`. The primitive is an invalid indexed pointer access, not an OOB write or demonstrated controlled overwrite.

* Reliable kernel crash / strong DoS: +1
  The invalid array access can lead to an invalid `link_sta` dereference or warning/oops path in a kernel wireless driver.

* Privileged kernel/device-management memory corruption path: +1
  The bug is in a trusted Wi-Fi driver path handling BA session state and firmware-mediated station mappings.

* Hard or state-dependent trigger: -1
  Triggering requires a specific inconsistent BA session state where `ba_data->sta_mask` becomes zero in these handlers. This is more constrained than a simple packet parser bug.

* Broad/common deployed exposure: +1
  Intel iwlwifi is broadly deployed, although the affected MLD BA session path is hardware and configuration dependent.

Paranoid additional signal:

* Weak LPE concern: +1
  The invalid station id can select an unintended pointer slot and lead to bogus object interpretation. This is not enough for a strong LPE claim, but it is enough to avoid auto-closing without manual review.

## 3. Reachability analysis

The most realistic attacker model is adjacent wireless influence, such as a malicious AP or peer condition that can affect BA session setup or teardown state. The issue is not reachable over the public Internet as a normal IP networking bug. No local account on the victim is necessarily required in the paranoid model, because the vulnerable state may be influenced through Wi-Fi protocol and firmware-mediated paths.

Namespaces and containers do not meaningfully lower or raise the main exposure, because the affected path is a physical Wi-Fi device driver rather than a namespace-local software interface. The path is only relevant on systems using affected Intel iwlwifi MLD-capable hardware and driver code. Call-site confidence: high, because the patch shows all three affected call sites and the immediate invalid index use.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is an out-of-bounds pointer-table access in a kernel wireless driver with adjacent external influence. The demonstrated impact is most clearly DoS through invalid pointer dereference or warning/oops behavior. Theoretical memory corruption concern exists because the invalid index can select an unintended object pointer, but the patch does not show an attacker-controlled write, controlled reclaim, callback control, or reliable object replacement. Therefore this is an Actionable Moderate at minimum, not a strong Important candidate on current evidence.

## 5. One-sentence report phrase

A zero sta_mask in iwlwifi MLD BA session handlers can make ffs() produce an invalid station id, causing an out-of-bounds access on fw_id_to_link_sta and a likely driver or kernel crash, with adjacent Wi-Fi or firmware-mediated triggering conditions requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is an OOB pointer access in a wireless driver with adjacent exposure and possible bogus object selection, even though the currently supported primitive is closer to DoS than proven privilege escalation.

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

Patch: wifi: iwlwifi: mld: validate sta_mask before ffs() in BA session handlers
Commit: 1de92789ce31e46fa7e7d8e89c90b19cdb1c103b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1de92789ce31e46fa7e7d8e89c90b19cdb1c103b

Commit description:

Three BA session handlers use ffs(ba_data->sta_mask) - 1 to derive a
station ID without checking that sta_mask is non-zero. When sta_mask is
zero, ffs() returns 0 and the subtraction wraps to 0xFFFFFFFF, causing
an out-of-bounds access on fw_id_to_link_sta[].

Add WARN_ON_ONCE(!ba_data->sta_mask) guards before each ffs() call,
consistent with the existing check in iwl_mld_ampdu_rx_start().

Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://patch.msgid.link/SYBPR01MB788115C6CE873271A9A15A25AF51A@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/wireless/intel/iwlwifi/mld/agg.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=1de92789ce31e46fa7e7d8e89c90b19cdb1c103b

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

The original Linux kernel CVE announcement for CVE-2026-64255 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64255

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: 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).