[CVE-2026-64338][MODERATE 7.0] USB: misc: uss720: unregister parport on probe failure

[CVE-2026-64338][MODERATE 7.0] USB: misc: uss720: unregister parport on probe failure

[AL-KERNEL]

CVE: CVE-2026-64338
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: USB: misc: uss720: unregister parport on probe failure
Commit: 6bbb98bec71b577fda4f4b48f7aea5874b04a576
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6bbb98bec71b577fda4f4b48f7aea5874b04a576
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64338
Analysis date: Sat, 25 Jul 2026 09:39:48 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate. Physical access limits exposure but stale registered object with freed private data should not be auto-closed
Manual review required: YES

Summary:
A probe error in the USB uss720 driver can leave a parport device registered with private data that is later freed, allowing a malicious or unsupported USB adapter to create a stale pointer condition that may lead to kernel crash and should be manually reviewed as a UAF candidate.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64338 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64338

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-2026-64338	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-772;CWE-404;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A stale parport registration in the uss720 USB probe error path can leave a registered parport device whose private data points to memory that is released after get_1284_register fails. A malicious or unsupported USB parallel adapter can trigger this during probe, and later parport access may dereference stale driver state and cause a kernel crash or a use after free condition. For the CVSS the PR:N is used because the vulnerable probe failure path can be reached by attaching or controlling the USB device without an authenticated local user, although physical access or control of attached USB hardware is required. The issue is not network reachable. Impact is at least denial of service. For the paranoid score, the stale private data pointer is treated as a UAF candidate with possible confidentiality and integrity impact, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate. Physical access limits exposure but stale registered object with freed private data should not be auto-closed (with actual score 4)	YES	USB SIMPLEFIX LEAK ERRORPATH HARDWARE LINUS TEST  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	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. Physical access limits exposure but stale registered object with freed private data should not be auto-closed**::

## 2. Signal breakdown

Conservative signals:

* External device mediated influence: +1. Triggering depends on an attached USB device or adapter behavior during probe, not on a network path.
* Memory corruption, weak or indirect corruption candidate: +1. The registered parport keeps `pp->private_data` pointing to driver private data that the error path releases.
* Real lifetime corruption: +1. This is a stale pointer after free / registered-object lifetime mismatch.
* Reliable kernel crash / strong DoS: +1. Later parport access can plausibly dereference freed driver state and crash the kernel.
* Weak LPE concern: +1. The stale pointer is a UAF candidate, but no controlled reclaim, overwrite, callback control, or object replacement is demonstrated.
* Physical-only or rare hardware-only condition: -2. The realistic trigger requires physical USB access or control of an attached USB parallel adapter.

Paranoid additional interpretation:

* Generic memory corruption as UAF candidate: upgraded from weak +1 to strong +2 only for paranoid scoring, because the patch explicitly describes a registered kernel object retaining a pointer to freed private data.
* Privileged kernel/device-management lifetime path: +1. The stale pointer exists in USB probe / parport device registration state, a trusted kernel device-management context.

## 3. Reachability analysis

The bug can be triggered during `uss720_probe()` when an unsupported or malicious USB parallel adapter causes `get_1284_register()` to fail after `parport_register_port()` has already registered the parport. No local authenticated user privileges are required in CVSS-style terms if the attacker can attach or emulate the USB device, but the attack is physical/device-local rather than network reachable.

Namespaces and containers do not significantly improve reachability unless the environment delegates USB device attachment or USB/IP-like device injection to an untrusted actor. The path is not a broad default remote exposure. It requires the `uss720` driver and compatible or intentionally malformed hardware behavior.

Call-site confidence: medium. The provided patch and commit message clearly describe the stale `pp->private_data` lifetime problem, but no later concrete dereference site, reclaim primitive, or exploit path is shown.

## 4. Severity interpretation

This behaves above an ordinary low-risk cleanup because it leaves a registered kernel-visible parport object with a pointer to freed driver private data. Realistic impact is most likely a physical-device-triggered kernel crash or persistent broken device state.

Theoretical memory-corruption potential exists because the stale pointer may be dereferenced after the private data is freed. However, practical privilege escalation is not demonstrated. There is no evidence of attacker-controlled reclaim, arbitrary write, callback hijack, or type confusion. Therefore the conservative score remains borderline, while the paranoid score reaches Actionable Moderate due to the explicit UAF-like lifetime condition.

## 5. One-sentence report phrase

A probe error in the USB uss720 driver can leave a parport device registered with private data that is later freed, allowing a malicious or unsupported USB adapter to create a stale pointer condition that may lead to kernel crash and should be manually reviewed as a UAF candidate.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch explicitly fixes a registered-object lifetime bug where `pp->private_data` can point to freed memory. Even though exposure is physical and no strong LPE primitive is shown, stale kernel object references after free should not be auto-closed without checking later parport access paths.

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

Patch: USB: misc: uss720: unregister parport on probe failure
Commit: 6bbb98bec71b577fda4f4b48f7aea5874b04a576
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6bbb98bec71b577fda4f4b48f7aea5874b04a576

Commit description:

uss720_probe() registers a parport before reading the 1284 register used
to detect unsupported Belkin F5U002 adapters. If get_1284_register()
fails, the error path drops the driver private data and the USB device
reference, but leaves the parport device registered.

Leaving the port registered is more than a private allocation leak:
parport_register_port() has already reserved a parport number and
registered the parport bus device, while pp->private_data still points at
the private data that the common error path is about to release.

Undo the pre-announce registration in the get_1284_register() failure
branch before jumping to the common private-data cleanup path. Clear
priv->pp first, matching the disconnect path and avoiding a stale pointer
in the private data.

This issue was identified during our ongoing static-analysis research while
reviewing kernel code.

Fixes: 3295f1b ("usb: misc: uss720: check for incompatible versions of the Belkin F5U002")
Cc: stable <stable@kernel.org>
Co-developed-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Ijae Kim <ae878000@gmail.com>
Signed-off-by: Myeonghun Pak <mhun512@gmail.com>
Reviewed-by: Alex Henrie <alexhenrie24@gmail.com>
Link: https://patch.msgid.link/20260706151049.63470-1-mhun512@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/misc/uss720.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=6bbb98bec71b577fda4f4b48f7aea5874b04a576

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

The original Linux kernel CVE announcement for CVE-2026-64338 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64338

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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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).