[CVE-2026-97576][MODERATE REGULAR] media: v4l2-ctrls: validate HEVC tile counts

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

CVE: CVE-2026-97576
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: media: v4l2-ctrls: validate HEVC tile counts
Commit: 400cd78a63cc647412cf069c9851bdea2818340c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=400cd78a63cc647412cf069c9851bdea2818340c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97576
Analysis date: Sat, 26 Sep 2026 15:27:14 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97576 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97576

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 REGULAR
Manual review required: NO

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
======================================================================

CVE-2026-97576	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97576 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-125;*CWE-20;*CWE-787;BEST CVSS score: '6.1';DESCR 'An out of bounds read can occur in stateless HEVC decoder drivers because V4L2_CTRL_TYPE_HEVC_PPS tile counts were not checked against the capacity of column_width_minus1 and row_height_minus1 arrays. A local user with access to a V4L2 stateless HEVC decode device can submit a PPS control with tiling enabled and excessive tile counts. The decoder may then read beyond the compound control structure and use invalid values as tile loop bounds. This can cause a kernel crash and may expose limited kernel data depending on the affected decoder driver and surrounding memory. For the CVSS the PR:L value is used because an attacker needs local access to the relevant V4L2 device node, commonly through video group membership or delegated device access. The issue is not directly network reachable. Impact is at least local denial of service. The out of bounds read primitive warrants manual review for driver specific disclosure or follow on memory safety effects. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	READ SIMPLEFIX HARDWARE LINUS 	YES	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

* +1 Local below-host-admin trigger. A local process with granted access to the relevant V4L2 stateless HEVC decoder device can submit V4L2_CTRL_TYPE_HEVC_PPS controls. This is below host-admin-equivalent privilege, although access is normally restricted by device-node permissions or video-group membership.
* +1 Weak kernel invalid-read primitive. The patch establishes that attacker-controlled tile counts could make stateless HEVC decoder drivers read past the fixed column_width_minus1 or row_height_minus1 arrays and consume the values as tile-loop bounds.

Important non-awarded signals:

* +0 Controlled reclaim is not demonstrated.
* +0 Arbitrary or directed kernel write is not demonstrated. CWE-787 is not supported by this patch alone because the fixed validation concerns reads from the tile-size arrays, not a write beyond those arrays.
* +0 Confidentiality is not awarded. An internal out-of-bounds read is established, but no path returning adjacent kernel bytes to userspace, the network, or a device-visible output is shown.
* +0 Integrity is not awarded. The patch does not establish an out-of-bounds write, active-object corruption, or an unauthorized modification primitive.
* +0 Reliable kernel crash is not independently awarded. Excessive tile-loop bounds can plausibly cause unsafe driver behavior or a crash, but the supplied commit contains no crash trace and does not establish a deterministic host-wide failure.
* +0 Remote reachability is not established. The vulnerable operation is reached through a local V4L2 ioctl control path.
* +0 Strong exploitation leverage is not established. No attacker-controlled replacement, callback, type confusion, refcount mutation, or useful post-read memory interpretation is shown.
* +0 No UAF, stale lifetime reference, double release, or repeated refcount mutation is established.

3. Reachability analysis

The evaluated attacker is a local user or process that can open a stateless HEVC V4L2 decoder device and submit codec controls. The vulnerable path is reachable through V4L2 control handling when tiling is enabled and the attacker provides excessive num_tile_columns_minus1 or num_tile_rows_minus1 values.

Host-admin-equivalent privilege is not required by the vulnerable ioctl itself. However, access to the relevant /dev/video device is deployment-dependent and is commonly controlled through device-node permissions, video-group membership, DRM/media services, containers with delegated devices, or similar local policy. This is sufficient evidence for HostAdminRequired=NO because the complete trigger can be performed by a non-administrative process once access to the device is granted.

Namespace-scoped privilege is unresolved. The supplied patch does not show that an attacker-created user or media namespace can independently create, expose, and operate the required stateless HEVC decoder device. No special hardware prerequisite is established beyond the existence of a supported stateless HEVC decoder driver and accessible video device. No race or narrow timing condition is involved.

4. Primitive and severity interpretation

The exact primitive is an attacker-controlled out-of-bounds read from fixed-size HEVC PPS tile-width or tile-height arrays. Stateless HEVC decoder drivers can use the unchecked count fields to read more entries than the uAPI structure contains and use the resulting values as tile-loop bounds.

This is not a UAF, lifetime violation, write primitive, ownership violation, or authorization bypass. It is not active structured-object reuse and it does not involve stale storage. The patch establishes an invalid input validation gap and a bounded-structure over-read, but does not establish that the adjacent data are disclosed or that their use produces a directed write or controllable corruption.

PrimitiveClass is CLASS_C because the demonstrated behavior is invalid-state processing with potential crash or denial-of-service consequences, without an independently useful memory-corruption primitive. ImportantCandidate is NO because the available evidence does not show controlled reuse, write capability, data disclosure, security-boundary impact, or privilege escalation. AutoDowngradeAllowed is YES because the patch-supported primitive is a read-only bounds violation with no demonstrated meaningful exploitation leverage beyond possible driver failure.

Likely operational severity is ordinary Moderate. Manual review remains recommended because individual stateless HEVC decoder implementations may consume invalid tile dimensions differently, and driver-specific surrounding code could establish a stronger crash or disclosure consequence not visible in this generic V4L2 validation patch.

5. One-sentence report phrase

Unchecked HEVC PPS tile counts could cause stateless V4L2 decoder drivers to read beyond fixed tile-dimension arrays, allowing a local user with access to a decoder device to trigger invalid kernel processing and potential denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The generic V4L2 validation bug establishes an out-of-bounds read, but the supplied patch does not include the affected decoder-driver call paths needed to determine whether any implementation exposes a reliable crash, data disclosure, or follow-on corruption effect.

7. Call-site confidence

Call-site confidence: medium

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

Patch: media: v4l2-ctrls: validate HEVC tile counts
Commit: 400cd78a63cc647412cf069c9851bdea2818340c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=400cd78a63cc647412cf069c9851bdea2818340c

Commit description:

The stateless HEVC decoders read num_tile_columns_minus1 + 1 entries from
column_width_minus1[] and num_tile_rows_minus1 + 1 from row_height_minus1[]
and use them as tile-loop bounds, but std_validate_compound() does not
bound these u8 counts. Reject a V4L2_CTRL_TYPE_HEVC_PPS with tiling
enabled whose tile counts exceed the uAPI array capacity, mirroring the
existing compound-control range checks.

Fixes: 256fa39 ("media: v4l: Add definitions for HEVC stateless decoding")
Assisted-by: Claude:claude-opus-4-8
Cc: stable@vger.kernel.org
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/media/v4l2-core/v4l2-ctrls-core.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=400cd78a63cc647412cf069c9851bdea2818340c

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

The original Linux kernel CVE announcement for CVE-2026-97576 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97576

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 6.1

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: 2

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 REGULAR

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).