[CVE-2026-98757][MODERATE 7.0] usb: cdns3: fix use-after-free in cdns3_gadget_exit()

[CVE-2026-98757][MODERATE 7.0] usb: cdns3: fix use-after-free in cdns3_gadget_exit()

[AL-KERNEL]

CVE: CVE-2026-98757
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: usb: cdns3: fix use-after-free in cdns3_gadget_exit()
Commit: cc448700db656cceb4b411bf99a2e7132144d035
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc448700db656cceb4b411bf99a2e7132144d035
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98757
Analysis date: Sat, 24 Oct 2026 04:53:35 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
Queued Cadence USB gadget work can execute after endpoint, buffer, and device teardown, causing a constrained kernel UAF and plausible host crash.

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

The original Linux kernel CVE announcement for CVE-2026-98757 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98757

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 7.0
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
======================================================================

CVE-2026-98757	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98757 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur because cdns3_gadget_exit releases endpoints aligned buffers and the final cdns3_device reference without first waiting for pending_status_wq and aligned_buf_wq. Both work handlers retain access to priv_dev related state after being queued. The pending status handler can also invoke an ep0 request completion after teardown. A queued handler running after the frees can dereference or modify reclaimed kernel memory and can at least crash the kernel. Reliable triggering requires a timing window between queued USB gadget work and controller teardown. For the CVSS the PR:L value in the paranoid vector reflects deployments where gadget lifecycle or USB role management is delegated to a local service or reduced capability process rather than requiring unrestricted root. Direct network reachability is not present and a remote network attacker cannot normally trigger this path. The concrete UAF justifies manual analysis for possible privilege escalation even though no controlled arbitrary write or demonstrated exploit is provided. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because 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 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 5 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 MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	USB UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no additional technically supported leverage.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Real UAF: queued work retains access to `priv_dev`; teardown frees endpoints, aligned buffers, and ultimately `priv_dev` without synchronously cancelling the work.
* +1 — Plausible kernel crash/strong DoS from a work handler dereferencing released device state.
* +0 — No timing penalty: a scheduling window is required, but the evidence does not establish that it is narrow, one-shot, or attacker-unrepeatable.
* +0 — No hardware rarity penalty: Cadence USB3 hardware is required, but it is not proven rare or physical-attacker-only.

Not awarded: controlled reclaim, attacker-shaped replacement contents, arbitrary/directed write, callback control, disclosure, LPE, or remote reachability. The ep0 completion call is not proof of attacker control over a reclaimed callback. There is no repeated release/refcount mutation on the same dangling reference, so no dedicated +1 or UAF floor 5. NEW52/B5-R, NEW53/B3-PENDING, and B4 authorization-state preservation do not apply.

3. Reachability analysis

The vulnerable sequence requires queued USB gadget work followed by controller/gadget teardown. The supplied evidence does not establish whether a normal user, delegated USB-role service, or only a host administrator can perform the complete lifecycle sequence; therefore host privilege is unknown and no privilege penalty or local-unprivileged bonus applies. No namespace-scoped capability path is shown. Trigger timing is race-dependent, but its practical difficulty and repeatability are unresolved.

4. Primitive and severity reading

This is a real asynchronous teardown UAF involving embedded work and structured `cdns3_device` state, not merely a warning or passive bookkeeping error. The stale use is nevertheless constrained to gadget teardown: no reclaim control or security-boundary crossing is shown. Patch-supported effects are stale dereference or modification and plausible host crash; exploitation beyond that is speculative. It is CLASS_B, but not presently a strong Important candidate. Auto-downgrade remains allowed because the evidence shows a constrained teardown UAF without a material unknown reuse primitive.

5. One-sentence report phrase

Queued Cadence USB gadget work can execute after endpoint, buffer, and device teardown, causing a constrained kernel UAF and plausible host crash.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm lifecycle permissions, work-handler operations, and whether gadget-controlled request state can provide useful post-free write or callback leverage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: usb: cdns3: fix use-after-free in cdns3_gadget_exit()
Commit: cc448700db656cceb4b411bf99a2e7132144d035
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc448700db656cceb4b411bf99a2e7132144d035

Commit description:

cdns3_gadget_start() arms two works on system_freezable_wq:
pending_status_wq for the deferred ep0 status stage and aligned_buf_wq
for realigned request buffers. Both handlers use the cdns3_device the
works are embedded in, and cdns3_pending_setup_status_handler() also
calls the ep0 request completion.

cdns3_gadget_exit() does not wait for these works. It frees all
endpoints and aligned buffers and drops the last reference to the
gadget device, which frees priv_dev, so a work queued before the exit
can run after the free.

Fix this by waiting for both works after the gadget driver is unbound
and the IRQ is freed, when no new work can be queued, and before the
endpoints and buffers are released.

This issue was found by an in-house static analysis tool.

Fixes: 7733f6c ("usb: cdns3: Add Cadence USB3 DRD Driver")
Cc: stable <stable@kernel.org>
Reported-by: Sicong Huang <congei42@163.com>
Closes: https://lore.kernel.org/linux-usb/7f5719b.8700.18f67b324d3.Coremail.congei42@163.com/
Suggested-by: Sicong Huang <congei42@163.com>
Assisted-by: Codex:gpt-5.6
Co-developed-by: Song Li <songl@zju.edu.cn>
Signed-off-by: Song Li <songl@zju.edu.cn>
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Acked-by: Peter Chen <peter.chen@kernel.org>
Link: https://patch.msgid.link/20260909095655.694527-1-fanwu01@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/cdns3/cdns3-gadget.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=cc448700db656cceb4b411bf99a2e7132144d035

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

The original Linux kernel CVE announcement for CVE-2026-98757 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98757

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 3

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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.
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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
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