[CVE-2026-98769][IMPORTANT] usb: gadget: f_uac1_legacy: validate bRequest index in generic_{set,get}_cmd

[CVE-2026-98769][IMPORTANT] usb: gadget: f_uac1_legacy: validate bRequest index in generic_{set,get}_cmd

[AL-KERNEL]

CVE: CVE-2026-98769
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: usb: gadget: f_uac1_legacy: validate bRequest index in generic_{set,get}_cmd
Commit: 36f3f009049bc91e14dc856007932473318d12f8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=36f3f009049bc91e14dc856007932473318d12f8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98769
Analysis date: Mon, 19 Oct 2026 03:53:13 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A malicious USB host can use crafted UAC1 SET_CUR or GET_CUR requests to perform a heap out of bounds write or read up to 44 bytes beyond con data, requiring mandatory review for adjacent object corruption, disclosure, kernel crash, and possible exploitation leverage.

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

The original Linux kernel CVE announcement for CVE-2026-98769 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98769

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-2026-98769	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98769 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, 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:H/A:H';CWE-129;CWE-125;*CWE-787;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'The legacy USB UAC1 gadget handlers derive an array index from the low four bits of bRequest but con data contains only five elements. A malicious USB host can select indices from 5 through 15 and trigger a heap out of bounds write through SET_CUR or a heap out of bounds read through GET_CUR, reaching up to 44 bytes beyond the array. The access occurs while processing a crafted class specific control request and does not require a race or another protocol stage. For the CVSS the PR:N value is used because the attacking USB host does not need an authenticated account or privileges on the target gadget. AV:P is used because exploitation requires a physical USB connection to a device exposing the legacy UAC1 gadget function and the issue is not reachable over an ordinary IP network. Impact includes kernel crash and potential disclosure or corruption of adjacent heap data. The controlled out of bounds write provides a plausible path to privilege escalation or kernel code execution, although reliable exploitation depends on the surrounding object layout and allocator behavior. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 6.8 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and V42_LEGACY_CLASSA_FD_VETO and MANUAL_REVIEW_REQUIRED and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 2.4 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. 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 IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	OOB USB SIMPLEFIX LINUS V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO V42_LEGACY_CLASSA_FD_VETO MANUAL_REVIEW_REQUIRED TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 5
* Raw paranoid score: 2
* Paranoid score: 5
* Applied conservative safety floor: 1 -> 5 because an attacker-influenced heap OOB write is directly established.
* Applied paranoid safety floor: 2 -> 5 for the same strong corruption primitive.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2 Strong corruption primitive. SET_CUR permits a malicious USB host to select indices 5 through 15 and write a host-influenced integer up to 44 bytes beyond the five-element heap array.
* +1 Confidentiality plausible. GET_CUR performs the corresponding OOB read, and normal control-request semantics provide a credible path for returning the selected value to the USB host.
* Paranoid only, +1 Reliable kernel crash or strong DoS. Repeated corruption of adjacent heap contents can realistically cause a kernel fault, although a deterministic panic is not demonstrated.

Negative signals:

* -2 Physical-only access and specialized device mode. The attacker must be the USB host physically connected to a target exposing the legacy UAC1 gadget function.

Important non-awarded signals:

* No arbitrary target, named adjacent victim, controlled reclaim, callback overwrite, credential modification, or completed privilege-escalation chain is established.
* No additional integrity point is awarded merely because adjacent heap bytes are corrupted.
* No extra availability point is awarded for the same potential kernel crash.
* NEW52 B5-R does not apply. The write is immediate and index-controlled, not accumulated across retries.
* V29 does not apply literally because this is not a descriptor-allocation sizing mismatch. The core OOB-write rules independently establish CLASS_A.
* V33 active-state trust-boundary promotion is not separately scored because no specific corrupted field and privileged downstream consumer are identified.
* B3-PENDING and B4-PENDING do not apply.

Arithmetic:

* Conservative: +2 OOB write +1 plausible disclosure -2 physical-only access = 1.
* Paranoid: +2 OOB write +1 plausible disclosure +1 potential kernel crash -2 physical-only access = 2.
* Both results are raised to 5 by the controlled-corruption manual-review safety floor.

3. Reachability analysis

The attacker is a malicious USB host connected to a Linux device configured to expose the legacy UAC1 gadget function. The host controls bRequest and can select an invalid index without authentication, target-side UID 0, capabilities, a race, or another protocol stage.

Configuring the target as a USB gadget normally requires prior owner or administrator setup, but this is a deployment prerequisite rather than a privilege held by the attacking USB host. The complete vulnerable request itself is therefore below target host-admin authority once the gadget is exposed.

The path is physical rather than IP-network reachable. User and network namespace capabilities are not relevant. Suitable USB gadget controller hardware and an active legacy UAC1 configuration are required. Repeated requests appear inexpensive and deterministic.

4. Primitive and severity interpretation

The exact primitives are:

* A bounded but attacker-influenced heap OOB write through `generic_set_cmd()`.
* A bounded heap OOB read through `generic_get_cmd()`.
* The attacker selects one of eleven invalid array positions and influences the written integer value.

This is active heap-object corruption, not a UAF, stale-storage defect, authorization bypass, retry-accumulated overwrite, or crash-only invalid dereference. The demonstrated consequence is modification or reading of memory up to 44 bytes beyond `con->data`.

Potential kernel crash and disclosure are credible. Privilege escalation or kernel code execution remains speculative because the adjacent object layout and downstream consumption are not supplied. Nevertheless, the directly established attacker-influenced heap write is CLASS_A and must not be automatically downgraded merely because physical access limits exposure or a complete exploit is unavailable.

ImportantCandidate is YES because the patch establishes controlled kernel heap corruption. AutoDowngradeAllowed is NO because automatic closure would discard the unresolved security significance of the adjacent heap overwrite.

5. One-sentence report phrase

A malicious USB host can use crafted UAC1 SET_CUR or GET_CUR requests to perform a heap out of bounds write or read up to 44 bytes beyond con data, requiring mandatory review for adjacent object corruption, disclosure, kernel crash, and possible exploitation leverage.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review the allocation and surrounding layout of `struct usb_audio_control`, the exact value encoding used by SET_CUR, whether GET_CUR returns all OOB bytes to the host, and whether repeated selected writes can modify pointers, callbacks, lengths, refcounts, or other active fields.

7. Call-site confidence

Call-site confidence: medium

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

Patch: usb: gadget: f_uac1_legacy: validate bRequest index in generic_{set,get}_cmd
Commit: 36f3f009049bc91e14dc856007932473318d12f8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=36f3f009049bc91e14dc856007932473318d12f8

Commit description:

generic_set_cmd() and generic_get_cmd() use the low nibble of
ctrl->bRequest as an index into con->data[]:

    u8 cmd = (ctrl->bRequest & 0x0F);  /* 0 .. 15 */
    ...
    con->data[cmd] = value;            /* OOB when cmd >= 5 */

struct usb_audio_control (include/linux/usb/audio.h) declares data as
a 5-element array, so indices 5 through 15 write (or read) up to 44
bytes past the end of the array on the heap.

A malicious USB host can craft a class-specific SET_CUR / GET_CUR
request with an arbitrary bRequest value, triggering the out-of-bounds
access from an IRQ completion handler with no further preconditions.

Add an ARRAY_SIZE() guard to both functions.

Fixes: c47d7b0 ("USB: audio: add USB audio class definitions")
Cc: stable <stable@kernel.org>
Reviewed-by: Weibin Liu <liuwb@xiaopeng.com>
Signed-off-by: Liu Chao <liuc63@xiaopeng.com>
Reviewed-by: Ivy Lopez <skunkolee@gmail.com>
Link: https://patch.msgid.link/20260921072551.3708191-1-liuc63@xiaopeng.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/linux/usb/audio.h
  drivers/usb/gadget/function/f_uac1_legacy.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=36f3f009049bc91e14dc856007932473318d12f8

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

The original Linux kernel CVE announcement for CVE-2026-98769 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98769

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:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 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: IMPORTANT
KPANIC detected for this report: NO
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).