[CVE-2026-98771][MODERATE REGULAR] usb: storage: sierra_ms: reject short SWoC info transfers

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

CVE: CVE-2026-98771
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: usb: storage: sierra_ms: reject short SWoC info transfers
Commit: c85e8331d298b8f1dee8fe63718e76435cec7133
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c85e8331d298b8f1dee8fe63718e76435cec7133
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98771
Analysis date: Sun, 18 Oct 2026 23:28:33 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A malicious USB device can use a short GetSwocInfo response to expose up to five bytes of stale kernel heap data per read through the world-readable truinst sysfs attribute.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98771 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98771

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 REGULAR
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-2026-98771	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98771 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N';*CWE-457;*CWE-200;CWE-252;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.6';DESCR 'A short USB GetSwocInfo IN transfer can leave the tail of a kmalloc allocated swoc_info structure uninitialized. The truinst sysfs handler later exposes the rev, LinuxSKU, and LinuxVer fields through a world readable attribute, allowing up to 5 bytes of stale kernel heap data to be disclosed per read. A malicious or emulated USB device with the expected VID and PID can trigger the condition repeatedly by returning a successful but incomplete response. For the CVSS the PR:N value is used because attaching the malicious peripheral does not require an authenticated privilege on the target and the resulting truinst attribute is readable by unprivileged userspace. The issue is not network reachable and normally requires physical access or prior control of an attached USB device. Impact is limited to confidentiality because no memory write, privilege escalation, or availability failure is established. Repeated reads may increase the practical value of the leak when init_on_alloc is disabled, so the possible disclosure of sensitive heap contents requires manual review. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.6 and the production ActionableScore returned 1 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.4 and ActionableScore 2 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 1)	MAYBE	USB INIT LEAK UAF HARDWARE LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=CONFIRMED
B4PendingReview=NO
B4PendingConfirmed=NO

## 1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

Arithmetic:

* +1 Confidentiality plausible because stale kernel heap bytes are copied to a world-readable sysfs attribute.
* +1 Local unprivileged trigger because reading `truinst` requires no privilege once the malicious device is attached.
* +1 Practical exploit chain because a short device response directly leads to disclosure through `truinst`.
* -2 Physical-only trigger because control of a connected malicious or emulated USB device is required.
* Total: 1.

The paranoid score is not increased. Repeated reads are established, but the patch does not prove that different or security-critical heap contents can be selected or recovered across reads.

## 2. Signal breakdown

Positive signals:

* +1: Concrete confidentiality impact. Up to five bytes of uninitialized `kmalloc-64` heap content reach unprivileged userspace per read.
* +1: Below-host-admin read path. The `truinst` attribute has mode `0444`.
* +1: Complete disclosure sequence. A short successful USB transfer leaves fields uninitialized and `truinst_show()` prints those fields.

Negative signals:

* -2: The malformed response requires control of a physically connected or emulated USB device with the expected VID and PID.

Important non-awarded signals:

* No UAF, OOB write, arbitrary write, controlled reclaim, refcount corruption, or callback influence is established.
* No integrity or availability consequence is established.
* No network reachability is established.
* No privilege escalation is established.
* Repeated reads do not receive an additional score because varying or attacker-selected stale contents are not demonstrated.
* NEW52 B5-R does not apply because there is no retry-accumulated heap OOB write or later consumption of corrupted structured state.
* NEW53 B3-PENDING does not apply because no shared-backing write exists.
* AuthorizationDecisionBypass is NO because the defect is missing transfer-length validation, not an authorization DENY-to-ALLOW transition.
* B4PendingReview and B4PendingConfirmed are NO.

## 3. Reachability analysis

A malicious or emulated USB device with VID `0x1199` and PID `0x0fff` must return a successful short response to `GetSwocInfo`. Once the driver accepts that response, any local user can read the world-readable `truinst` sysfs attribute and receive the stale bytes.

The complete path does not require host UID 0 or host-administrator capabilities when the attacker has physical USB access and an ordinary local account. It is not namespace-dependent, not remotely network-triggerable, and does not require a race. Kernels using `init_on_alloc` may neutralize or substantially reduce the stale-data exposure.

## 4. Primitive and severity interpretation

The exact primitive is a bounded but repeatable disclosure of uninitialized kernel heap data. A short USB IN transfer initializes only part of `struct swoc_info`, after which `truinst_show()` exports fields overlapping the uninitialized tail.

This is neither an OOB read nor memory corruption. The kernel reads bytes that are inside the allocated object but were not initialized by the device transfer. The demonstrated consequence is disclosure of up to five stale bytes per sysfs read. Disclosure of changing sensitive data across repeated allocations is plausible but not established.

`PrimitiveClass=CLASS_B` is used for the concrete security-relevant disclosure primitive. It is not Class A because substantial or attacker-directed kernel disclosure is not demonstrated. `ImportantCandidate=NO` because physical access is required and the leak is narrowly bounded. `AutoDowngradeAllowed=NO` preserves manual inspection because the disclosure is indefinite, directly user-visible, and may expose sensitive slab contents when `init_on_alloc` is disabled.

## 5. One-sentence report phrase

A malicious USB device can use a short GetSwocInfo response to expose up to five bytes of stale kernel heap data per read through the world-readable truinst sysfs attribute.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Confirm whether repeated initialization or reattachment cycles expose changing heap contents, whether sensitive `kmalloc-64` objects can precede the allocation, and whether affected product kernels enable `init_on_alloc`.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: usb: storage: sierra_ms: reject short SWoC info transfers
Commit: c85e8331d298b8f1dee8fe63718e76435cec7133
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c85e8331d298b8f1dee8fe63718e76435cec7133

Commit description:

sierra_get_swoc_info() requests sizeof(struct swoc_info) (60) bytes
from the device via usb_control_msg(), but its callers only treat a
negative return value as failure. A device that answers the
vendor-specific GetSwocInfo request with a short IN transfer is
therefore accepted, leaving the tail of the freshly allocated
(kmalloc(), non-zeroing) swoc_info buffer uninitialized.

truinst_show() subsequently prints swocInfo->rev, swocInfo->LinuxSKU
and swocInfo->LinuxVer from that buffer into the world-readable
(0444) "truinst" sysfs attribute. An emulated/malicious USB device
(VID 0x1199, PID 0x0fff) can exploit this to disclose up to 5 bytes
of stale kernel heap memory (kmalloc-64) to unprivileged userspace,
once per sysfs read, indefinitely. On kernels built without
init_on_alloc this leaks recently freed heap contents.

Only accept the transfer when the full structure was received.
sierra_ms_init() already retries failed queries, so well-behaved
devices are unaffected.

Fixes: 32fe5e3 ("USB Storage Sierra: TRU-Install feature update")
Cc: stable <stable@kernel.org>
Signed-off-by: Syed Labeeq Sajid Bukhari <syedlabeeq@gmail.com>
Assisted-by: Kimi:K2 [Kimi Code CLI]
Link: https://patch.msgid.link/20260910140343.49371-1-syedlabeeq@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/storage/sierra_ms.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=c85e8331d298b8f1dee8fe63718e76435cec7133

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

The original Linux kernel CVE announcement for CVE-2026-98771 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98771

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 4.6

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

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).