[CVE-2026-64037][IMPORTANT] wifi: iwlwifi: mld: fix TSO segmentation explosion when AMSDU is disabled [ Upstream

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

CVE: CVE-2026-64037
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: wifi: iwlwifi: mld: fix TSO segmentation explosion when AMSDU is disabled [ Upstream
Commit: 9e360e610a73f62432e986775023d5382773f045
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e360e610a73f62432e986775023d5382773f045
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64037
Analysis date: Sun, 19 Jul 2026 17:52:16 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An iwlwifi MLD TSO arithmetic bug can turn an AMSDU-disabled sentinel value into gso_size 0, causing a massive segmentation burst and TX completion storm that may lead to TCP skb lifetime corruption, UAF, refcount underflow, and kernel crash.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64037 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64037

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: IMPORTANT
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-2026-64037	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-682;**CWE-400;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'An integer corner case in the iwlwifi MLD TSO path can make num_subframes become zero when AMSDU is disabled for a TID and max_tid_amsdu_len is set to the sentinel value 1. The zero value can propagate into the TSO segmentation helper as gso_size 0, causing skb_gso_segment to create a very large number of tiny segments from one GSO skb and flooding the TX path. The described failure mode includes memory corruption and a subsequent use after free in the TCP retransmit queue, with refcount underflow in tcp_shifted_skb and possible NULL dereference in tcp_rack_detect_loss. For the CVSS the PR:N is used in the paranoid score because an adjacent wireless attacker or malicious AP may be able to influence the wireless link state that disables AMSDU, while normal traffic from the victim can exercise the transmit path. The issue is not Internet routable and is best treated as adjacent or local depending on the deployment. Impact is at least denial of service via kernel crash and may include confidentiality or integrity impact if the UAF is controllable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE OOB DANGER UAF NETWORK SKB KPANIC 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. AMSDU disablement comes from TLC or firmware driven station state rather than a direct userspace value.
* Local unprivileged trigger: +1. A local user may be able to generate TCP GSO traffic over the affected Wi-Fi device once the bad AMSDU state exists.
* Weak LPE concern: +1. The commit describes memory corruption and UAF symptoms, but does not demonstrate attacker-controlled reclaim, replacement, or write control.
* Memory corruption, strong primitive: +2. The described downstream failure includes memory corruption and a use-after-free in TCP retransmit handling.
* Real lifetime corruption: +1. The failure mode includes UAF and refcount underflow in TCP skb handling.
* Reliable kernel crash / strong DoS: +1. NULL dereference and TX completion storm make kernel crash realistic.
* Hard or condition-dependent trigger: -1. Requires iwlwifi MLD, AMSDU disabled sentinel state, GSO/TSO traffic, and the specific segmentation path.
* Corruption primitive constrained or not yet controlled: -1. The patch does not show an attacker-controlled payload, target selection, or reclaim primitive.

Conservative total: 5.

Paranoid additions / changes:

* Privilege escalation plausible, stronger interpretation: +2 instead of +1. UAF plus refcount underflow in TCP skb lifetime code is a class that deserves manual review even without a published exploit primitive.
* Broad deployed exposure: +1. Intel Wi-Fi and TCP/GSO transmit paths are common enough that this should not be treated as an obscure-only issue.

Paranoid total: 8.

Call-site confidence: medium. The patch shows the immediate arithmetic and fallback site, while the deeper TCP UAF path is described by the commit message rather than fully shown in the diff.

## 3. Reachability analysis

The most realistic trigger is local unprivileged traffic generation over an affected Intel iwlwifi MLD device after AMSDU has been disabled for a TID. A malicious or unusual wireless environment may influence the firmware/TLC state that disables AMSDU, but the bug is not Internet-routable and should not be treated as ordinary AV:N remote reachability.

Namespaces and containers may matter if a containerized workload can send traffic through the host Wi-Fi device, but the hardware and driver state remain host-controlled. No CAP_SYS_ADMIN or CAP_NET_ADMIN is inherently required just to generate TCP traffic, so PR:L is realistic for the local path. For the paranoid interpretation, PR:N-like adjacent influence is considered only through malicious AP or wireless environment control plus victim traffic, not as direct remote packet parsing.

The path is not universally enabled on all systems because it requires the iwlwifi MLD subdriver and affected hardware/firmware behavior. Still, the affected components are common enough that this should not be auto-closed as niche.

## 4. Severity interpretation

This behaves above ordinary Moderate because the commit does not merely describe a WARN or resource exhaustion. It explicitly connects the segmentation explosion to memory corruption, TCP retransmit queue UAF, refcount underflow, and NULL dereference.

Realistically demonstrated impact is strong DoS and kernel crash under specific Wi-Fi and traffic conditions. Theoretical impact includes possible LPE if the UAF or refcount corruption can be shaped into controlled object reuse, but that is not demonstrated by the patch. Therefore the conservative score is Actionable Moderate, while the paranoid score is a Strong Important candidate for manual review.

## 5. One-sentence report phrase

An iwlwifi MLD TSO arithmetic bug can turn an AMSDU-disabled sentinel value into gso_size 0, causing a massive segmentation burst and TX completion storm that may lead to TCP skb lifetime corruption, UAF, refcount underflow, and kernel crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch context explicitly mentions memory corruption and UAF in TCP retransmit handling, and the affected path is reachable through ordinary traffic once the Wi-Fi driver reaches the AMSDU-disabled state.

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

Patch: wifi: iwlwifi: mld: fix TSO segmentation explosion when AMSDU is disabled [ Upstream
Commit: 9e360e610a73f62432e986775023d5382773f045
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e360e610a73f62432e986775023d5382773f045

Changed files:
  drivers/net/wireless/intel/iwlwifi/mld/tx.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=9e360e610a73f62432e986775023d5382773f045

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

The original Linux kernel CVE announcement for CVE-2026-64037 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64037

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 5
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).