[CVE-2026-93083][LOW] firmware: arm_scmi: Unwind TX receiver mailbox setup failure [ Upstream

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

CVE: CVE-2026-93083
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: firmware: arm_scmi: Unwind TX receiver mailbox setup failure [ Upstream
Commit: babb017cf5e4600c94c23ea87175a0380235a3ee
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=babb017cf5e4600c94c23ea87175a0380235a3ee
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93083
Analysis date: Fri, 18 Sep 2026 01:58:29 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93083 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93083

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-93083	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93083 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:H/UI:N/S:U/C:N/I:N/A:H';*CWE-772;CWE-404;CWE-459;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'SCMI mailbox setup can leak the primary mailbox channel when the optional unidirectional Tx receiver channel request fails after the primary channel was already acquired. This leaves the primary channel busy and can make later probe attempts fail or defer indefinitely, causing loss of SCMI functionality and a local availability impact. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over driver probing, platform firmware configuration, or device setup. The issue is not network reachable and does not provide a direct memory corruption primitive. Impact is denial of service to the affected SCMI transport or dependent firmware services.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	INIT SIMPLEFIX HARDWARE LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0. No floor or cap applied.
* Raw paranoid score: 1
* Paranoid score: 1. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +1 Concrete persistent kernel resource/reference leak. The primary mailbox channel is acquired and then not released when the optional TX receiver channel request fails.
* +1 Limited availability impact. The leaked busy channel can cause later probe attempts to fail or defer, affecting SCMI transport availability.
* -2 Host-admin-equivalent or platform-management prerequisite. Reliable triggering is tied to driver probe, probe deferral, mailbox setup, or platform firmware/device configuration, not an ordinary user interface.

Paranoid signals:

* +1 Concrete persistent kernel resource/reference leak. Same as conservative.
* +1 Availability impact. Same as conservative.
* +1 Broader platform availability concern. SCMI may back firmware services such as power, clock, or performance control on affected ARM platforms, so a stuck probe can have operational impact beyond one ordinary device.
* -2 Host-admin-equivalent or platform-management prerequisite. Same as conservative.

Important non-awarded signals:

* RealUAF not awarded. The patch shows a leaked mailbox channel, not use after free.
* CLASS_A or CLASS_B corruption not awarded. No memory corruption, stale dereference, double release, refcount mutation, arbitrary write, or controlled reclaim is established.
* Remote reachability not awarded. The path is firmware and driver probe setup, not network packet processing.
* Local unprivileged trigger not awarded. No ordinary user reachable interface for the complete trigger is established.
* Extra resource exhaustion escalation not awarded. The leak is concrete, but there is no evidence of unprivileged repeated accumulation to host-wide exhaustion.
* C or I impact not awarded. No disclosure, unauthorized modification, or security-boundary bypass is shown.

3. Reachability analysis

The vulnerable path is `mailbox_chan_setup()` in the ARM SCMI mailbox transport during channel setup. A realistic trigger requires influencing driver probing, probe deferral, mailbox availability, firmware description, or platform device setup. That is normally host administrator or platform-management territory.

No namespace-scoped capability path is established. No ordinary user interface, syscall, netlink path, or network path is shown. Prior platform configuration and the presence of SCMI mailbox transport are prerequisites. This is not a race. The issue is an ordered error-unwind failure after the second mailbox channel request fails.

4. Primitive and severity interpretation

The exact primitive is a missing unwind of an already acquired mailbox channel. It is a resource/reference leak and not an active structured UAF. There is no cleanup stale dereference and no concrete repeated release/refcount operation.

PrimitiveClass is NONE because no meaningful corruption, ownership bypass, authorization bypass, UAF, or semantic security primitive is established. The demonstrated consequence is that the primary mailbox channel remains busy, which can block later probe attempts and cause local SCMI functionality loss. The speculative worst case is broader platform service unavailability if the affected SCMI transport is critical on that device.

ImportantCandidate is NO because this is a host-admin-reachable resource cleanup issue without memory corruption or security-boundary impact. AutoDowngradeAllowed is YES because unresolved Important-grade exploitation leverage is not present.

5. One-sentence report phrase

A failed SCMI TX receiver mailbox setup can leak the already acquired primary mailbox channel, leaving it busy for later probe attempts and causing local firmware transport availability impact without memory corruption or network reachability.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an ordinary low-end availability/resource-cleanup issue because the patch establishes only a leaked mailbox channel on a privileged probe/setup path.

7. Call-site confidence

Call-site confidence: high

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

Patch: firmware: arm_scmi: Unwind TX receiver mailbox setup failure [ Upstream
Commit: babb017cf5e4600c94c23ea87175a0380235a3ee
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=babb017cf5e4600c94c23ea87175a0380235a3ee

Changed files:
  drivers/firmware/arm_scmi/transports/mailbox.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=babb017cf5e4600c94c23ea87175a0380235a3ee

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

The original Linux kernel CVE announcement for CVE-2026-93083 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93083

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: 0
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).