[CVE-2026-89892][MODERATE 7.0] media: em28xx: defer audio-only extension registration

[CVE-2026-89892][MODERATE 7.0] media: em28xx: defer audio-only extension registration

[AL-KERNEL]

CVE: CVE-2026-89892
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: media: em28xx: defer audio-only extension registration
Commit: 0da1e627f4fc9d0e947fdae90913042120878923
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0da1e627f4fc9d0e947fdae90913042120878923
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89892
Analysis date: Wed, 16 Sep 2026 12:44:27 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89892 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89892

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-2026-89892	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89892 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-672;*CWE-664;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'A use-after-free in the em28xx USB media driver can occur because audio-only extension registration may happen before the optional secondary device is fully constructed. On a dual-TS board the secondary device can inherit is_audio_only and be inserted into em28xx_devlist as an independent entry, although extension operations are expected to reach it through dev_next from the primary device. During disconnect the secondary device can be freed while its list node remains reachable, leaving a stale kernel pointer that may be used by later extension callbacks. For the CVSS the PR:N is selected because no privileges on the target system are required if the attacker can present a crafted or affected USB device to the host. The issue is not network reachable in normal deployments and requires physical or local USB device access. Impact is at least denial of service via kernel crash and in the paranoid model may include confidentiality and integrity impact because the bug class is kernel use-after-free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	DANGER USB INIT UAF HARDWARE LINUS SYZBOT KPANIC 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 4
* Raw paranoid score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

Conservative arithmetic: +2 real UAF, +1 realistic kernel crash / DoS, -2 physical or local USB device access requirement = 1. Applied conservative UAF floor 4 because a real stale kernel object remains reachable from a global device list and host-admin privilege is not required.

Paranoid arithmetic: +2 real UAF, +1 realistic kernel crash / DoS, +1 unresolved active structured stale-object callback/list traversal concern, -2 physical or local USB device access requirement = 2. Applied paranoid UAF floor 5 because the stale secondary device is not merely a fixed async buffer and remains reachable through em28xx_devlist for later extension operations.

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation: the secondary em28xx device can be freed during disconnect while its list node remains reachable in em28xx_devlist.
* +1 Reliable kernel crash / strong DoS: later traversal or extension callback use of the freed device can produce a kernel UAF fault.
* +1 Paranoid active structured stale-object concern: the stale object is a structured driver device object linked into a global list and later extension operations may consume it. This is not counted as controlled reclaim or arbitrary write.

Negative signals:

* -2 Physical or local USB device access: the attacker needs to present or control an affected/crafted em28xx USB device path. No network trigger is established.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary write is not demonstrated.
* Information disclosure is not demonstrated.
* Remote network reachability is not established.
* Concrete repeated release/refcount mutation is not established.
* Extra availability point is not awarded because the same kernel crash is already counted.
* Strong LPE leverage is not awarded because no callback hijack, controlled replacement, or attacker-shaped reclaimed object is shown.
* C/I are not awarded as direct ActionableScore bonuses merely because UAF could theoretically corrupt reclaimed memory.

Repeated release/refcount check:

* First release can end lifetime: yes, the secondary device can be freed during disconnect.
* Exact same reference survives: a stale list node remains reachable through em28xx_devlist.
* Second operation is a real lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, only in paranoid scoring due to active structured stale-object list/callback exposure, not due to repeated release.

3. Reachability analysis

The realistic attacker is a physical or local USB-device attacker who can connect or emulate an affected em28xx dual-TS/audio-only device and drive probe/disconnect behavior. No host administrator privilege is required if the attacker can present the device to the host, so HostAdminRequired=NO.

This is not namespace-scoped. Network namespaces, user namespaces, and CAP_NET_ADMIN are not material to the trigger. NamespaceScopedPrivilege=NO.

The complete trigger depends on the em28xx USB driver being present and an affected device path being probed. This is hardware/device specific, but the evidence does not show a purely host-admin-only configuration step. The main reducing factor is physical or local USB access rather than privilege.

The race/timing aspect is not the main issue. The bug is an ordering/lifetime bug: extension registration occurs before dev_next construction, allowing the duplicate secondary device to be independently inserted into the global list.

4. Primitive and severity interpretation

The exact primitive is a real use-after-free of a structured em28xx device object reachable through em28xx_devlist. The stale storage is not just a fixed transfer buffer. It is an active structured object whose list membership can make it reachable by later extension operations.

The demonstrated consequence is kernel memory lifetime violation and likely crash/DoS. The speculative consequence is broader kernel memory corruption if the freed object storage is reused and later extension traversal consumes meaningful fields, but controlled reclaim or attacker-controlled replacement is not established.

PrimitiveClass=CLASS_B because this is a real kernel lifetime/UAF primitive, but not a demonstrated Class A primitive. ImportantCandidate=YES because a stale structured device object remains globally reachable and exploitation leverage beyond crash is unresolved. AutoDowngradeAllowed=NO because automatically closing this as ordinary crash-only Moderate would discard a concrete unresolved kernel UAF in active driver state.

Likely operational severity is Actionable Moderate, with Strong Important review warranted if further analysis shows controlled reclaim, useful field consumption after reuse, callback influence, or a practical local USB exploit chain.

5. One-sentence report phrase

A real use-after-free in the em28xx USB media driver can leave a freed secondary device reachable through em28xx_devlist after disconnect, allowing later extension operations to dereference stale kernel state and cause at least a local USB triggered kernel crash.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch directly establishes a real kernel UAF involving a structured device object and a stale global list entry. Physical/local USB access limits exposure, but unresolved post-free list/callback behavior should not be auto-downgraded.

7. Call-site confidence

Call-site confidence: medium

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

Patch: media: em28xx: defer audio-only extension registration
Commit: 0da1e627f4fc9d0e947fdae90913042120878923
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0da1e627f4fc9d0e947fdae90913042120878923

Commit description:

The audio-only path registers extensions while probing the primary device.
For a dual-TS board, this happens before dev_next is created. The duplicate
device inherits is_audio_only and is then independently inserted into
em28xx_devlist.

The list is intended to contain only primary devices: extension operations
reach the secondary device through dev_next. The independently linked
secondary can be freed during disconnect while its list node remains
reachable, resulting in a use-after-free.

Defer audio-only extension registration to the module-request work item. It
runs only after probing has completed construction of the optional
secondary device, so only the primary is registered and extension callbacks
reach the secondary through dev_next.

Fixes: 4a08966 ("media: em28xx-cards: rework the em28xx probing code")
Cc: stable@vger.kernel.org
Reported-by: syzbot+a11c46f37ee083a73deb@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/66ec3c83.050a0220.29194.002f.GAE@google.com/T/
Suggested-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Diego Fernando Mancera Gomez <diegomancera.dev@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/usb/em28xx/em28xx-cards.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=0da1e627f4fc9d0e947fdae90913042120878923

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

The original Linux kernel CVE announcement for CVE-2026-89892 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89892

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:L/I:L/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: 4
  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: 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).