[CVE-2026-89894][IMPORTANT] media: cx231xx: reject geometry changes while the VBI queue is busy

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

CVE: CVE-2026-89894
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: media: cx231xx: reject geometry changes while the VBI queue is busy
Commit: aa3314506deb9703bcf0e889db08959440228fbf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa3314506deb9703bcf0e889db08959440228fbf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89894
Analysis date: Wed, 16 Sep 2026 08:55:55 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89894 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89894

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: IMPORTANT
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-2026-89894	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89894 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-362;CWE-367;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An out-of-bounds write in the cx231xx VBI capture path can occur because format and TV standard changes update device wide geometry while only the video queue is checked for busy state. A local user with access to the V4L2 video and VBI device nodes can allocate a VBI buffer with one geometry, keep the VBI queue active, then change width or norm through the video node so cx231xx_do_vbi_copy() computes offsets using a larger live geometry than the allocated plane. For the CVSS the PR:L means the attacker needs local access to the media device node, for example membership in a group that can open the V4L2 device or equivalent delegated device access. The issue is not network reachable and requires the affected cx231xx hardware and VBI streaming path. Impact is at least local denial of service via kernel memory corruption and kernel crash, and because the primitive is a kernel heap out-of-bounds write with attacker influenced offset it may plausibly lead to privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	WRITE OOB USB HARDWARE LINUS KPANIC MEMORY 	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6
* Raw paranoid score: 7
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate**::

No floor or cap was applied.

2. Signal breakdown

Positive signals:

* +2 Strong corruption primitive. The patch context establishes a real kernel heap out-of-bounds write in `cx231xx_do_vbi_copy()`, where `memcpy(plane + offset, p_buffer, lencopy)` can write past the allocated VBI plane.
* +1 Local below-host-admin trigger. The issue is reachable by a local application with access to the affected V4L2 video and VBI device nodes, not by host-admin-only kernel management.
* +1 Reliable kernel crash / strong DoS. Kernel heap corruption from an out-of-bounds write can realistically crash the host kernel.
* +1 Weak LPE concern. This is more than a generic crash because the offset is attacker-influenced through geometry changes, and the write lands past a kernel heap buffer.
* +1 Memory layout invariant violation. The allocated VBI plane size is based on old `dev->width` / `dev->norm`, while the later copy offset is computed from live changed geometry.

Paranoid-only signal:

* +1 Stronger exploitation concern. The primitive is a kernel heap out-of-bounds write with attacker-influenced offset, so Important-grade exploitation cannot be dismissed even though the payload is device-derived and full target control is not demonstrated.

Non-awarded or constrained signals:

* RealUAF not awarded. This is an OOB write, not a use-after-free.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Fully attacker-controlled payload not demonstrated because copied bytes come from the device data path.
* Remote reachability not established.
* Extra Availability not awarded because the crash/DoS is already counted.
* Confidentiality and Integrity are not separately awarded as proven consequences, but integrity risk is represented by the established heap overwrite primitive and manual-review classification.
* Hardware-specific deployment is noted, but no strong physical-only penalty is applied because the vulnerable operation is exposed through normal V4L2 device-node use once affected hardware is present.

3. Reachability analysis

The evaluated attacker is a local user or local process with access to the affected cx231xx V4L2 video and VBI device nodes. The attacker can prepare a smaller VBI buffer, keep the VBI queue busy, and then change video geometry or standard through the video node because the old code checked only `dev->vidq` and not `dev->vbiq`.

Host administrator privilege is not positively required for the vulnerable ioctl sequence once the device nodes are accessible. This is not a namespace-scoped capability issue. It depends on affected cx231xx hardware and the VBI streaming path being available. The issue is not directly network reachable. The bug is not primarily a hard race. It is an allowed state transition where device-wide geometry changes while an already allocated VBI buffer remains active.

4. Primitive and severity interpretation

The exact primitive is a kernel heap out-of-bounds write past a VBI videobuf2 plane. The stale condition is not object lifetime reuse but a geometry mismatch: buffer allocation and preparation use one geometry, while the later URB completion copy computes offsets using a newer live geometry.

This is active kernel buffer corruption, not fixed crash-only metadata corruption. The write target is constrained by heap layout and buffer placement, and the payload comes from the device stream, but the offset is attacker-influenced through `dev->width` and `dev->norm`. That makes it stronger than a pure NULL dereference or WARN-only issue.

PrimitiveClass is CLASS_A because an attacker-influenced kernel heap OOB write is directly established. Demonstrated consequence is local kernel memory corruption and likely DoS. Speculative but technically defensible consequence is local privilege escalation if the heap overwrite can be shaped into corruption of useful adjacent kernel state. ImportantCandidate is YES because the primitive is strong enough to require Important-vs-Moderate review. AutoDowngradeAllowed is NO because automatically closing this as ordinary Moderate would discard a concrete kernel heap overwrite primitive.

5. One-sentence report phrase

A local user with access to the affected cx231xx V4L2 video and VBI device nodes can change device-wide geometry while the VBI queue is active, causing an attacker-influenced kernel heap out-of-bounds write and requiring manual review for possible privilege escalation.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a real kernel heap out-of-bounds write with attacker-influenced offset, and although full payload or target control is not proven, the primitive is too strong for automatic downgrade.

7. Call-site confidence

Call-site confidence: high

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

Patch: media: cx231xx: reject geometry changes while the VBI queue is busy
Commit: aa3314506deb9703bcf0e889db08959440228fbf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa3314506deb9703bcf0e889db08959440228fbf

Commit description:

vidioc_s_fmt_vid_cap() and vidioc_s_std() change the device-wide
dev->width / dev->norm but only refuse the change when the *video* queue
(dev->vidq) is busy. The VBI queue (dev->vbiq) shares that same geometry:
cx231xx_init_vbi_isoc() latches dma_q->lines_per_field from dev->norm,
the VBI videobuf2 plane is sized from dev->width / dev->norm in
vbi_queue_setup() and vbi_buf_prepare(), and cx231xx_do_vbi_copy() then
recomputes the destination offset from the *live* dev->width and the
latched lines_per_field on every URB completion:

	offset = lines_completed * (dev->width << 1) + ...;
	if (dma_q->current_field == 2)
		offset += dev->width * 2 * dma_q->lines_per_field;
	memcpy(plane + offset, p_buffer, lencopy);

Because the VBI node shares video_ioctl_ops with the video node, an
application can size a small VBI plane (REQBUFS/QBUF with a small width,
or with the NTSC standard), then enlarge dev->width (or switch dev->norm
to PAL) through the video node while the VBI stream is running -- the
change is allowed because only dev->vidq is checked -- and let the device
deliver a field-2 VBI payload. cx231xx_do_vbi_copy() now computes the
offset with the larger geometry and memcpy()s past the end of the smaller
plane that was already allocated, a heap out-of-bounds write whose offset
is attacker-chosen and whose contents come from the device. The
per-field guard in cx231xx_copy_vbi_line() does not help: it bounds the
copy against the latched lines_per_field, not the plane's real capacity,
and vb2 does not re-run buf_prepare() for an already prepared buffer.

Refuse the format/standard change when the VBI queue is busy as well, so
the geometry cannot change underneath an allocated VBI buffer.

Fixes: 7c61713 ("media: cx231xx: convert to the vb2 framework")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/usb/cx231xx/cx231xx-video.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=aa3314506deb9703bcf0e889db08959440228fbf

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

The original Linux kernel CVE announcement for CVE-2026-89894 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89894

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:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).