* [CVE-2026-93120][MODERATE REGULAR] usb: gadget: configfs: fix out-of-bounds read of qw_sign [ Upstream
@ 2026-09-18 0:44 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 0:44 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93120
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: usb: gadget: configfs: fix out-of-bounds read of qw_sign [ Upstream
Commit: b895dbed8ac9e12a5ffa1a2165575a8469f8340d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b895dbed8ac9e12a5ffa1a2165575a8469f8340d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93120
Analysis date: Thu, 17 Sep 2026 20:44:40 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A bounded out-of-bounds read in the USB gadget configfs `qw_sign` attribute can expose up to 14 adjacent kernel-object bytes through local configfs access when the stored UTF16 signature lacks a NUL terminator.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93120 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93120
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-93120 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-93120 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';CWE-125;*CWE-200;CWE-131;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'An out-of-bounds read in the USB gadget configfs OS descriptor qw_sign attribute occurs because a byte length was used as a UTF16 code unit count. If qw_sign is filled without a NUL terminator, os_desc_qw_sign_show can read past the 14 byte array into following gadget_info fields and expose adjacent kernel object bytes through the configfs attribute. For the CVSS the PR:L is used in the paranoid score because some systems may delegate gadget configfs control to a service account, container root, or reduced capability administrator rather than full host root. The issue is not network reachable and is triggered through local configfs access. Impact is limited confidentiality loss from a bounded adjacent object read, with no clear evidence of integrity impact, availability impact, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES OOB USB SIMPLEFIX LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
## 1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap changed the score.
## 2. Signal breakdown
Positive signals:
* +1 Concrete bounded read-only OOB primitive. `os_desc_qw_sign_show()` used a byte length as a UTF-16 code-unit count, allowing reads up to 14 bytes past `gi->qw_sign`.
* +1 Confidentiality plausible. The over-read bytes are converted and exposed through the configfs attribute output, so this is a real local information-disclosure path.
Negative signals:
* No negative privilege penalty applied. USB gadget configfs is typically administrator-controlled, but the supplied evidence does not fully prove the complete trigger always requires host-admin-equivalent privilege.
* No race/timing penalty. This is deterministic length misuse, not a timing race.
* No rare-hardware penalty. USB gadget mode is configuration-dependent, but the patch does not establish rare physical hardware as a material requirement.
Important non-awarded signals:
* RealUAF not awarded. No lifetime violation or stale object use is shown.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Integrity impact not awarded. The store-side fix corrects the output code-unit limit, but the supplied context does not establish an actual OOB write because the input length is already bounded.
* Availability impact not awarded. No crash, panic, or persistent DoS is established.
* CLASS_A not used. The disclosure is bounded and adjacent-object only, not substantial kernel disclosure.
* ImportantCandidate not set. The primitive is a small local OOB read with limited disclosure and no demonstrated escalation path.
## 3. Reachability analysis
The vulnerable path is reached through the USB gadget configfs `qw_sign` attribute. A user who can cause `qw_sign` to be filled without a NUL terminator and then read the attribute can receive bytes from adjacent fields in `struct gadget_info`.
In normal deployments, USB gadget configfs management is usually restricted to root or a privileged service. However, the patch alone does not prove the exact permission model for all deployments, nor whether an already-created gadget exposes the readable attribute to a lower-privileged actor. Therefore `HostAdminRequired=UNKNOWN`.
No network trigger is established. This is local configfs access, not USB host packet processing and not remote network input.
No namespace-scoped privilege is established. The issue is not shown to be reachable through attacker-created namespaces.
Prior privileged setup may exist in real deployments because a gadget usually has to be configured before the attribute exists, but this is deployment-specific and not scored as a proven host-admin requirement from the supplied patch alone.
Race repeatability is not relevant. The bug is deterministic once the attribute state is suitable.
## 4. Primitive and severity interpretation
The exact primitive is a bounded read-only out-of-bounds access from `gi->qw_sign` into following members of `struct gadget_info`, with the resulting bytes exposed through a configfs read.
This is not active structured UAF and not fixed stale storage. It is a local information disclosure caused by a length-unit mismatch between bytes and UTF-16 code units.
There is no concrete repeated release/refcount operation. No first lifetime operation frees an object, no dangling reference survives, and no second lifetime/refcount mutation occurs.
Primitive class is `CLASS_C` because the issue is a weak read-only OOB disclosure primitive without memory corruption, write capability, lifetime corruption, authorization bypass, or demonstrated privilege escalation.
Demonstrated consequence: limited local kernel-object information disclosure.
Speculative consequence: leaked adjacent bytes might marginally assist other attacks, but no direct exploitation chain, KASLR bypass, credential leak, or LPE path is established.
`ImportantCandidate=NO` because the patch supports only a small bounded disclosure. `AutoDowngradeAllowed=YES` because there is no unresolved strong corruption, ownership, lifetime, or authorization primitive.
Likely operational severity is Low to ordinary Moderate, depending mainly on whether gadget configfs access is delegated to non-root users or services.
## 5. One-sentence report phrase
A bounded out-of-bounds read in the USB gadget configfs `qw_sign` attribute can expose up to 14 adjacent kernel-object bytes through local configfs access when the stored UTF16 signature lacks a NUL terminator.
## 6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Manual review is recommended to confirm actual configfs permissions and whether the product delegates USB gadget management to non-root users, but the patch-supported primitive remains limited information disclosure.
## 7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: gadget: configfs: fix out-of-bounds read of qw_sign [ Upstream
Commit: b895dbed8ac9e12a5ffa1a2165575a8469f8340d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b895dbed8ac9e12a5ffa1a2165575a8469f8340d
Changed files:
drivers/usb/gadget/configfs.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=b895dbed8ac9e12a5ffa1a2165575a8469f8340d
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93120 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93120
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:L/PR:H/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS score: 3.3
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: 2
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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