[CVE-2026-64344][MODERATE 7.0] USB: idmouse: fix use-after-free on disconnect race

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

CVE: CVE-2026-64344
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: USB: idmouse: fix use-after-free on disconnect race
Commit: 31e75fed8f90cfea9f8285e7ed135b0e452bf872
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31e75fed8f90cfea9f8285e7ed135b0e452bf872
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64344
Analysis date: Sat, 25 Jul 2026 13:07:19 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
USB idmouse has a local disconnect versus release race where driver data can be freed while mutex_unlock() may still access the embedded mutex, creating a kernel UAF with likely DoS impact and limited but nonzero manual-review LPE concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64344 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64344

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
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CVE-2026-64344	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'USB idmouse has a disconnect race where idmouse_release() and idmouse_disconnect() can drop the last reference while mutex_unlock() may still access the mutex object after the unlock operation. This is a use-after-free candidate in driver private data lifetime handling and can cause a kernel crash. For the CVSS the PR:L is used because a local user or process needs access to the idmouse character device or an equivalent local device context to race release with USB disconnect. The issue is not network reachable and requires a local or physical USB device scenario. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because the freed driver object contains a mutex and other fields that can be accessed after free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	LOCK USB INIT NOMEMCHK RACE UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process that can open the idmouse character device can participate in the release side of the race.
* Memory corruption, weak primitive: +1. This is a race-dependent UAF around driver-private object lifetime and mutex_unlock(), but no attacker-controlled reclaim, overwrite, callback control, or type confusion is shown.
* Real lifetime corruption: +1. The patch replaces open/present lifetime handling with kref, confirming a real object lifetime bug.
* Reliable kernel crash / strong DoS: +1. A UAF in mutex_unlock() can plausibly crash the kernel.
* Hard or unreliable race / special timing required: -1. The bug requires release() to race with USB disconnect().
* Rare and difficult-to-reach subsystem/configuration: -1. The affected idmouse USB device is uncommon and requires the device path to be present.

Paranoid additions / differences:

* Availability impact realistic: +1. A successful trigger affects kernel stability system-wide.
* Rare-hardware penalty is not applied in the paranoid score because environments with the device attached expose the vulnerable local device path directly.

Not awarded:

* No remote/network trigger.
* No strong LPE bonus. The patch shows UAF risk, but not reclaim control, write-after-free, function-pointer control, object replacement, or type confusion.
* No strong memory-corruption primitive. This matches the race-UAF downgrade rule.

## 3. Reachability analysis

A local user or local process needs access to the idmouse device node and must race file release with USB disconnect. Physical access or an equivalent local USB hotplug/reset scenario is likely needed for reliable triggering. Namespaces do not obviously make this broadly reachable unless the device node is explicitly passed into a container. The path is not default-exposed on most systems because it depends on uncommon USB idmouse hardware and device-node permissions.

Call-site confidence: high. The patch includes open(), release(), probe(), disconnect(), and the object-free path.

## 4. Severity interpretation

This behaves above an ordinary low-priority cleanup because it fixes a concrete UAF in kernel object lifetime handling. Realistic impact is most likely local DoS through kernel crash. Theoretical LPE concern exists because it is a kernel UAF, but the patch does not show a practical exploit primitive such as attacker-controlled reclaim, overwrite, callback dispatch, or type confusion. Therefore it is best treated as Borderline to Actionable Moderate, not a strong Important candidate by default.

## 5. One-sentence report phrase

USB idmouse has a local disconnect versus release race where driver data can be freed while mutex_unlock() may still access the embedded mutex, creating a kernel UAF with likely DoS impact and limited but nonzero manual-review LPE concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
Reason: this is a real kernel UAF race in device lifetime handling, even though exploitation beyond DoS is not demonstrated and exposure is limited by rare hardware and local/physical triggering conditions.

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

Patch: USB: idmouse: fix use-after-free on disconnect race
Commit: 31e75fed8f90cfea9f8285e7ed135b0e452bf872
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31e75fed8f90cfea9f8285e7ed135b0e452bf872

Commit description:

mutex_unlock() may access the mutex structure after releasing the lock
and therefore cannot be used to manage lifetime of objects directly
(unlike spinlocks and refcounts). [1][2]

Use a kref to release the driver data to avoid use-after-free in
mutex_unlock() when release() races with disconnect().

[1] a51749a ("locking/mutex: Document that mutex_unlock() is
                   non-atomic")
[2] 2b9d9e0 ("locking/mutex: Clarify that mutex_unlock(), and most
                   other sleeping locks, can still use the lock object
                   after it's unlocked")

Fixes: 54d2bc0 ("USB: fix locking in idmouse")
Cc: stable@vger.kernel.org	# 2.6.24
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260622152612.116422-3-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/misc/idmouse.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=31e75fed8f90cfea9f8285e7ed135b0e452bf872

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

The original Linux kernel CVE announcement for CVE-2026-64344 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64344

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:L/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: 3
  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: MODERATE
KPANIC detected for this report: NO
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).