[CVE-2026-68206][MODERATE 7.0] media: v4l2-ctrls: validate HEVC active reference counts

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

CVE: CVE-2026-68206
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: media: v4l2-ctrls: validate HEVC active reference counts
Commit: 9a998cc1c348769262d433acb7d238c5fac4b2e0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a998cc1c348769262d433acb7d238c5fac4b2e0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68206
Analysis date: Mon, 10 Aug 2026 16:50:09 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed HEVC stateless V4L2 slice control can provide active reference counts beyond the maximum DPB size, allowing a local process with decoder device access to trigger driver-specific invalid reference-list handling and likely DoS, with limited OOB impact possible in affected drivers.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68206 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68206

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-2026-68206	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:L/A:H';*CWE-20;CWE-125;*CWE-787;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'A malformed HEVC stateless V4L2 slice control can provide active L0 or L1 reference counts that exceed the maximum DPB entry count. The common validation path did not reject these counts before driver specific decode code consumed the control, so a local userspace process with access to the V4L2 decoder device could make a driver process an invalid reference list size. For the CVSS the PR:L is used because the attacker needs local access to a V4L2 device node or to a media service that queues these controls, but full administrator privileges are not normally required in systems where video devices are delegated to users or sandboxed media processes. The issue is not directly network reachable. Impact is at least local denial of service through a driver crash or hardware decode failure, and in the paranoid score it may allow limited confidentiality or integrity impact if a specific driver turns the invalid count into an out of bounds access.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	OOB SIMPLEFIX HARDWARE LINUS  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 at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process with access to the V4L2 stateless HEVC decoder device can queue malformed HEVC slice controls.
* Memory corruption, weak/indirect corruption candidate: +1. The unchecked active L0/L1 reference counts can be consumed by driver-specific code as array bounds or loop limits, but the patch does not show a concrete write primitive.
* Availability impact realistic: +1. A malformed reference count can plausibly crash or wedge a media decoder driver or hardware decode path.

Paranoid additional signals:

* Confidentiality impact plausible: +1. If a specific driver uses the invalid count for reads from reference-list or DPB-related arrays, limited OOB read behavior is plausible.
* Integrity impact plausible: +1. If a specific driver uses the invalid count while constructing hardware command buffers or per-frame metadata, limited OOB write or metadata corruption is possible.

Capping and constraints:

* This is primarily an input-validation fix, so conservative scoring is capped below Important without a concrete downstream primitive.
* No strong memory-corruption primitive is demonstrated in the patch.
* No arbitrary write, UAF, double-free, type confusion, callback control, or attacker-controlled reclaim is shown.
* Call-site confidence: medium. The common validation path is visible, but the driver-specific consumers are not included in the provided patch.

## 3. Reachability analysis

The bug is locally reachable through V4L2 stateless HEVC decoder controls, typically via `/dev/video*` device nodes. Full root privileges are not necessarily required because video devices are commonly delegated to users, media services, sandboxed browser or codec processes, or members of a `video`-like group.

The issue is not directly network reachable. A remote file or stream could only become relevant if it is decoded by a local process that forwards attacker-controlled HEVC parameters into the V4L2 stateless decoder API.

The affected path is configuration and hardware dependent. It requires a stateless HEVC V4L2 decoder driver and userspace using these controls. This is not a universal kernel path, but it is reachable through ordinary local media interfaces on systems with supported hardware.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary low-risk validation bug. The realistic impact is local DoS through driver crash, decode failure, or hardware pipeline failure.

The theoretical risk is higher because the invalid count is consumed by driver-specific code and may affect array indexing or metadata construction. However, without a shown OOB write, UAF, or controllable corruption sink, it should not be treated as a Strong Important candidate solely from this patch.

The paranoid score is justified for manual-review sensitivity because a shared validation gap affects multiple stateless HEVC drivers, and some driver implementations may turn the invalid reference count into limited OOB read or write behavior.

## 5. One-sentence report phrase

A malformed HEVC stateless V4L2 slice control can provide active reference counts beyond the maximum DPB size, allowing a local process with decoder device access to trigger driver-specific invalid reference-list handling and likely DoS, with limited OOB impact possible in affected drivers.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the patch fixes common validation before driver-specific consumption, and the real impact depends on how individual stateless HEVC drivers use `num_ref_idx_l0_active_minus1` and `num_ref_idx_l1_active_minus1`.

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UPSTREAM PATCH SUMMARY
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Patch: media: v4l2-ctrls: validate HEVC active reference counts
Commit: 9a998cc1c348769262d433acb7d238c5fac4b2e0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a998cc1c348769262d433acb7d238c5fac4b2e0

Commit description:

HEVC slice parameters are shared stateless V4L2 controls, but the common
validation path does not verify the active L0/L1 reference counts before
driver-specific code consumes them.

The original report came from Cedrus, but the active count bounds are
not Cedrus-specific. Validate them in the common HEVC slice control path
so stateless HEVC drivers get the same basic guarantees as soon as the
control is queued.

Do not reject ref_idx_l0/ref_idx_l1 entries here. Existing userspace may
use out-of-range sentinel values such as 0xff for missing references, and
some hardware can use that information for concealment. Keep this common
check limited to the active reference counts.

Fixes: d395a78 ("media: hevc: Add decode params control")
Cc: stable@vger.kernel.org
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@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=9a998cc1c348769262d433acb7d238c5fac4b2e0

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

The original Linux kernel CVE announcement for CVE-2026-68206 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68206

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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).