[CVE-2026-46199][MODERATE 7.0] drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg

[CVE-2026-46199][MODERATE 7.0] drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg

[AL-KERNEL]

CVE: CVE-2026-46199
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg
Commit: c72a8b4dc6d598e3831ef3abd9c6527dfbf4810e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c72a8b4dc6d598e3831ef3abd9c6527dfbf4810e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46199
Analysis date: Sat, 01 Aug 2026 10:17:36 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A local user with access to the AMDGPU DRM render node can craft a VCN4 decoder message in a GPU BO that causes out-of-bounds reads during kernel-side parsing, leading at least to local DoS and possibly limited information or parser-state impact.

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

The original Linux kernel CVE announcement for CVE-2026-46199 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46199

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: 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
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CVE-2026-46199	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-125;*CWE-20;CWE-129;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.6';DESCR 'The AMDGPU VCN4 decoder message parser can read out of bounds while parsing a user controlled decoder message stored in a GPU BO. A local user with access to the DRM render node can craft a message where the header length, buffer count, or buffer offsets make vcn_v4_0_dec_msg read past the valid message or BO range. For the CVSS the PR:L is selected because triggering requires local code execution and access to the amdgpu DRM interface, but does not normally require full administrator privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include limited confidentiality or integrity impact from OOB read influenced parser state, but the patch does not support an arbitrary write or a direct privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-46199  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB SIMPLEFIX HARDWARE KPANIC 	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local user with access to the amdgpu DRM render node can plausibly submit a crafted BO and command stream reaching the VCN decoder message parser.

* Reliable kernel crash / strong DoS: +1
  The parser can read past the valid message or BO range. A malformed message can plausibly cause a kernel fault or crash during command submission validation.

* Confidentiality impact plausible: +1
  The primitive is read-only OOB. There is no direct disclosure path shown, but limited confidentiality concern is defensible because the kernel parser may read adjacent BO or mapped memory contents.

* Broad/default/common exposure: +1
  DRM render nodes are commonly exposed to local users on systems with affected AMD GPUs. This is hardware-specific, but not an obscure privileged-only code path on affected machines.

Paranoid additional signal:

* Integrity impact plausible: +1
  OOB-read values may influence parser state, buffer selection, or validation decisions. This is weak and indirect, so it does not justify LPE or strong memory-corruption scoring, but it supports Actionable Moderate handling.

Not awarded:

* Remote reachable: +0
  This is not network-triggerable.

* Strong memory corruption primitive: +0
  The patch shows OOB reads and bounds validation, not OOB writes, UAF, double-free, arbitrary write, or type confusion.

* Privilege escalation plausible: +0
  No reclaim, overwrite, callback control, refcount abuse, or direct LPE primitive is shown.

* High-control device API bonus: +0
  This is a GPU ioctl path, but the patch does not show attacker control over object lifetime, callback targets, refcounts, DMA mappings, or page ownership sufficient for the extra bonus.

## 3. Reachability analysis

The likely trigger is a local user able to submit AMDGPU command streams through the DRM render node. This usually means PR:L rather than PR:H because render nodes are commonly available to non-root users through desktop, compute, or media workloads. Containers can also matter if `/dev/dri/renderD*` is passed into the container.

The path is not remotely reachable by packet traffic. It requires an affected AMDGPU VCN4-capable device and the relevant decoder command submission path. This is hardware-dependent, but on affected systems the interface is a normal local GPU interface rather than a rare debug-only configuration.

Call-site confidence: medium. The patch shows the parser and bounds checks, but not the full command-submission call chain.

## 4. Severity interpretation

This behaves stronger than an ordinary Moderate because it is a local, user-reachable kernel parser OOB read in a commonly exposed DRM device path. Realistic impact is primarily local DoS, with limited confidentiality concern from read-only OOB behavior.

It does not currently look like an Important-class vulnerability because the patch does not show write corruption, UAF, object replacement, callback control, or a concrete privilege-escalation primitive. The paranoid score is kept at Actionable Moderate to avoid auto-closing a local kernel OOB-read parser bug that may need manual review.

## 5. One-sentence report phrase

A local user with access to the AMDGPU DRM render node can craft a VCN4 decoder message in a GPU BO that causes out-of-bounds reads during kernel-side parsing, leading at least to local DoS and possibly limited information or parser-state impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a local user-reachable GPU driver OOB read in a kernel parser. The currently visible primitive is not enough for Important-class LPE, but it is actionable and should not be auto-closed without checking the surrounding command submission and BO mapping behavior.

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

Patch: drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg
Commit: c72a8b4dc6d598e3831ef3abd9c6527dfbf4810e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c72a8b4dc6d598e3831ef3abd9c6527dfbf4810e

Commit description:

Check bounds against the end of the BO whenever we access the msg.

Signed-off-by: Benjamin Cheng <benjamin.cheng@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/vcn_v4_0.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=c72a8b4dc6d598e3831ef3abd9c6527dfbf4810e

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

The original Linux kernel CVE announcement for CVE-2026-46199 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46199

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: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: 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).