[CVE-2026-89739][MODERATE 7.0] usb: dwc3: gadget: Fix use-after-free in dwc3_gadget_free_endpoints due to race condition

[CVE-2026-89739][MODERATE 7.0] usb: dwc3: gadget: Fix use-after-free in dwc3_gadget_free_endpoints due to race condition

[AL-KERNEL]

CVE: CVE-2026-89739
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: usb: dwc3: gadget: Fix use-after-free in dwc3_gadget_free_endpoints due to race condition
Commit: 448e95c0f3eaa8d99f16ccae92ab94545f14413b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=448e95c0f3eaa8d99f16ccae92ab94545f14413b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89739
Analysis date: Fri, 11 Sep 2026 16:59:05 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A race in the DWC3 USB gadget cleanup path can leave `nostream_work` pending after `dep` is freed, allowing delayed work to access freed kernel memory and cause a local or device-mediated denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-89739 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89739

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.

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

CVE-2026-89739	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89739 CHECK WITH IMPACT FROM ORIG NN MODERATE	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;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free race exists in the DWC3 USB gadget endpoint cleanup path because delayed nostream_work can remain pending or running after the endpoint object has been freed. A NoStream endpoint event can queue the delayed work, while gadget teardown can later free the same dep object, allowing dwc3_nostream_work to access freed kernel memory. For the CVSS the PR:L is used for the paranoid score because reduced capability root, service accounts, or delegated USB gadget management may be enough to trigger gadget teardown while USB events are pending. The issue is not network reachable over IP and normally requires local control of gadget teardown and or physical USB interaction with the device. Impact is at least denial of service via kernel crash, and in the paranoid interpretation the UAF may allow confidentiality and integrity impact if freed memory is reused in a controllable way.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	USB RACE UAF HARDWARE DEBUGFS KPANIC 	YES	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

Conservative floor applied: 3 -> 4 due to a real kernel UAF with stale reference use and no positively established host-admin-only requirement.

## 2. Signal breakdown

Positive signals:

* +2 Real UAF / lifetime violation: `dep->nostream_work` may remain pending or running after `dep` is freed by `kfree(dep)`.
* +1 Reliable kernel crash / strong DoS: delayed work handler `dwc3_nostream_work` can access freed endpoint state, making kernel fault or crash realistic.
* +1 Device-mediated external influence, paranoid only: the stale work can be queued from a USB gadget endpoint stream event, so an attached USB host or controller event participates in reaching the vulnerable path.

Negative signals:

* -1 Conservative timing constraint: the issue depends on an async workqueue and teardown ordering between endpoint stream event handling and gadget removal.

Material non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary read/write not demonstrated.
* Concrete repeated release/refcount mutation not established.
* Structured stale-object leverage not awarded because the supplied evidence only shows delayed work using freed `dep`, not attacker-shaped replacement fields or callback control.
* Weak LPE not awarded merely because the bug is a UAF.
* Extra Availability not awarded because the same crash is already counted.
* C/I impact not awarded in ActionableScore because the patch establishes UAF and DoS, but not disclosure, arbitrary write, controlled reuse, or privilege escalation.

Repeated-release/refcount check:

* First release can end lifetime: yes, `kfree(dep)` ends the endpoint object lifetime.
* Exact same reference survives: yes, embedded `dep->nostream_work` can remain queued and identifies the freed object.
* Second operation is a lifetime/refcount mutation: no, the stale operation is delayed work execution, not a second `put`, `release`, `free`, or refcount mutation.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage awarded: no.
* FLOOR 5 applied: no.

## 3. Reachability analysis

The vulnerable sequence requires a DWC3 USB gadget endpoint to receive a `DEPEVT_STREAM_NOSTREAM` event that queues `nostream_work`, followed by gadget teardown that frees endpoint objects before the delayed work has completed.

The complete trigger likely requires local control over USB gadget removal or unbind, and possibly cooperation or influence from the USB host side to generate the NoStream event. In common deployments, gadget configuration and teardown are privileged operations, often performed through configfs, driver unbind, or device-management paths. However, the supplied patch text does not fully prove host-admin-equivalent privilege for every deployment, so `HostAdminRequired=UNKNOWN` rather than `YES`.

No namespace-scoped privilege path is established. This is not IP-network reachable. It is USB/device-local and control-plane driven. There is no evidence that an ordinary unprivileged local user can complete the full trigger chain. The race is not purely theoretical, but the supplied evidence points to an async teardown/workqueue ordering issue rather than a broadly repeatable unprivileged data-plane trigger.

## 4. Primitive and severity interpretation

The exact primitive is a real use-after-free: a delayed work item embedded in or associated with `struct dwc3_ep` can run after the endpoint object `dep` has been freed.

The stale object is an active structured driver object rather than a passive scalar value, but the supplied evidence only shows post-free work execution and likely crash. The stale path is tied to gadget teardown and delayed work cleanup. It is not a demonstrated controlled-reclaim, arbitrary-write, callback-hijack, refcount-takeover, or privilege-escalation primitive.

Primitive class is `CLASS_B`: real kernel lifetime corruption exists, but exploitation leverage beyond crash is not established. Demonstrated consequence is DoS through kernel crash or fault. Speculative consequence is broader memory corruption if freed memory is reused in a favorable way, but that is not sufficiently supported for additional ActionableScore points.

`ImportantCandidate=NO` because this looks like a constrained async cleanup/teardown UAF with no concrete reuse or second lifetime mutation. `AutoDowngradeAllowed=YES` because the unresolved primitive does not currently show meaningful exploitation leverage beyond crash. Operationally, this is best treated as borderline to actionable Moderate, with manual review recommended due to explicit UAF.

## 5. One-sentence report phrase

A race in the DWC3 USB gadget cleanup path can leave `nostream_work` pending after `dep` is freed, allowing delayed work to access freed kernel memory and cause a local or device-mediated denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: explicit kernel UAF exists, but the supplied evidence indicates a constrained teardown/workqueue crash path without controlled reclaim, repeated refcount mutation, arbitrary read/write, or demonstrated privilege escalation.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: usb: dwc3: gadget: Fix use-after-free in dwc3_gadget_free_endpoints due to race condition
Commit: 448e95c0f3eaa8d99f16ccae92ab94545f14413b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=448e95c0f3eaa8d99f16ccae92ab94545f14413b

Commit description:

In dwc3_gadget_init_endpoint, &dep->nostream_work is bound with
dwc3_nostream_work, and dwc3_gadget_endpoint_stream_event can queue
this delayed work on system_percpu_wq when a DEPEVT_STREAM_NOSTREAM
event is received.

If we remove the gadget, dwc3_gadget_free_endpoints makes cleanup and
the memory allocated for dep with kzalloc() is released by kfree(dep),
while the delayed work mentioned above may still be pending or
running. The sequence of operations that may lead to a UAF bug is as
follows:

CPU0                                      CPU1

                                          | dwc3_thread_interrupt
                                          | dwc3_endpoint_interrupt
                                          | dwc3_gadget_endpoint_stream_event
                                          | queue_delayed_work(system_percpu_wq,
                                          |                    &dep->nostream_work)
dwc3_gadget_free_endpoints                |
dwc3_free_trb_pool(dep)                   |
list_del(&dep->endpoint.ep_list)          |
dwc3_debugfs_remove_endpoint_dir(dep)     |
kfree(dep)                                |
// dep is freed                           |
                                          | dwc3_nostream_work
                                          | // use dep (use-after-free)

Fix it by canceling the delayed work before kfree(dep) in
dwc3_gadget_free_endpoints.

Fixes: dcfe437 ("usb: dwc3: gadget: Reinitiate stream for all host NoStream behavior")
Assisted-by: Codex:deepseek-v4-flash
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Cc: stable@vger.kernel.org
Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Link: https://patch.msgid.link/331d1d5133496d2b4184e05f8848adb06930a138.1785893865.git.xiaopei01@kylinos.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/dwc3/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=448e95c0f3eaa8d99f16ccae92ab94545f14413b

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

The original Linux kernel CVE announcement for CVE-2026-89739 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89739

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: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: 4

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.
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).