[CVE-2026-80909][MODERATE 7.0] drm/amdgpu: Reject UVD message with invalid number of h265 refs

[CVE-2026-80909][MODERATE 7.0] drm/amdgpu: Reject UVD message with invalid number of h265 refs

[AL-KERNEL]

CVE: CVE-2026-80909
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/amdgpu: Reject UVD message with invalid number of h265 refs
Commit: 1facad2a78c1a8aeecc36eb4d560c7f1e10ce198
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1facad2a78c1a8aeecc36eb4d560c7f1e10ce198
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80909
Analysis date: Fri, 04 Sep 2026 14:42:42 -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-2026-80909 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80909

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-2026-80909	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80909 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:H/I:H/A:H';CWE-190;*CWE-20;*CWE-787;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.8';DESCR 'An invalid H.265 reference count in an AMDGPU UVD command message can make num_dpb_buffer exceed the expected decoder limit and can overflow the later min_dpb_size calculation. This may let an invalid command stream pass buffer size validation with undersized DPB or context buffers, which can result in GPU faults, GPU reset, or a kernel level denial of service. For the CVSS the PR:L is used because a local user process with access to the DRM render node or GPU device can submit UVD command streams without full administrator privileges. The issue is not network reachable and requires local access to the graphics device interface. Impact is at least local denial of service, and the paranoid score treats the integer overflow as a plausible memory corruption or out of bounds GPU memory access candidate that may affect confidentiality or integrity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-80909 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

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

1. ActionableScore

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

No floor or cap changed the score.

2. Signal breakdown

Conservative positive signals:

* +1 Local unprivileged trigger. AMDGPU UVD command submission is normally reachable by a local user process with access to the DRM render node or GPU device, not necessarily by host administrator only.
* +1 Weak or indirect corruption candidate. The attacker controlled H.265 reference count can exceed the expected decoder limit and affects a later DPB size calculation.
* +1 Memory layout invariant restoration. The patch restores consistency between the validated number of DPB buffers and the minimum DPB or context buffer size calculation.
* +1 Reliable device or kernel DoS concern. An undersized accepted decode buffer can plausibly lead to GPU fault, GPU reset, or kernel level denial of service.

Paranoid additional signal:

* +1 Weak exploitation leverage concern. The integer overflow is in a size calculation used for buffer validation, so an invalid command stream may pass with undersized buffers and create an out of bounds GPU memory access candidate.

Non-awarded signals:

* RealUAF not awarded. No use after free or stale lifetime operation is shown.
* Concrete repeated release or refcount not awarded. There is no first release followed by a second lifetime mutation on the same reference.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Strong LPE leverage not awarded. The patch supports an overflow and buffer validation bypass candidate, but not controlled kernel object corruption or credential manipulation.
* Remote reachability not established. This is a local DRM GPU interface path.
* Extra availability not awarded. GPU fault or crash is counted once.
* C/I impact is not treated as established for the conservative score. It is only part of the paranoid interpretation because of the possible undersized buffer and OOB access candidate.

3. Reachability analysis

The likely attacker is a local user process that can submit AMDGPU UVD command streams through the DRM render node or another accessible GPU device interface. This is below host administrator in common desktop and workstation deployments where render nodes are exposed to logged in users or users in the render or video group.

HostAdminRequired is NO because the vulnerable operation is command submission to the GPU decode path, not a mount, module load, or host wide administrator operation. NamespaceScopedPrivilege is NO because this is not primarily a namespace capability issue.

There is no direct network trigger. Remote exploitation would require an additional application level path that feeds attacker controlled media decode work into a local GPU decoding process, but that is outside the supplied kernel patch evidence.

Special AMD GPU hardware and UVD support are required, but consumer and workstation AMD GPUs are not rare enough to justify a hardware rarity penalty. No race or special timing condition is involved.

4. Primitive and severity interpretation

The exact primitive is an integer overflow or invalid size calculation caused by accepting an H.265 reference count above the expected UVD decoder limit. The value is read from the UVD message and used as num_dpb_buffer. Without the new check, num_dpb_buffer can exceed 17 and later influence min_dpb_size and min_ctx_size calculations.

This is not an active structured object UAF and not fixed stale storage. It is a buffer validation and memory layout invariant bug in a GPU command processing path.

PrimitiveClass is CLASS_B because the patch establishes a real corruption candidate that needs exploitation leverage review: attacker influenced input can make a size calculation overflow and may allow undersized buffers to pass validation. The demonstrated practical consequence is at least local denial of service through GPU or kernel fault. The speculative but defensible consequence is OOB GPU memory access with possible confidentiality or integrity impact depending on firmware behavior, buffer placement, and GPU memory isolation.

ImportantCandidate is YES because this should not be automatically downgraded as a simple validation bug. The calculation is security relevant and may gate buffer size checks before hardware or firmware access.

AutoDowngradeAllowed is NO because the unresolved primitive is an attacker influenced integer overflow in a buffer size validation path, with plausible memory corruption or OOB access consequences.

Likely operational severity is actionable Moderate, with manual review needed to decide whether it rises to Important based on actual downstream buffer use and GPU memory access behavior.

5. One-sentence report phrase

An invalid H.265 reference count in AMDGPU UVD command processing can overflow the DPB size calculation and may let an undersized decode buffer pass validation, causing local DoS and requiring manual review for possible OOB GPU memory access impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch is small, but it protects a size calculation used for buffer validation before GPU video decode processing. This is not proven LPE, but it is strong enough to avoid automatic closure.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/amdgpu: Reject UVD message with invalid number of h265 refs
Commit: 1facad2a78c1a8aeecc36eb4d560c7f1e10ce198
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1facad2a78c1a8aeecc36eb4d560c7f1e10ce198

Commit description:

Same change as for h264, avoids overflow later when calculating
min dpb size.

Signed-off-by: David Rosca <david.rosca@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit a4b0720 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_uvd.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=1facad2a78c1a8aeecc36eb4d560c7f1e10ce198

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

The original Linux kernel CVE announcement for CVE-2026-80909 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80909

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: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: 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).