[CVE-2026-74443][MODERATE 7.0] drm/vmwgfx: bound DMA command body size against suffix pointer

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

CVE: CVE-2026-74443
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/vmwgfx: bound DMA command body size against suffix pointer
Commit: 036e16ada95389bdc30f41068af04c1d0872fad0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=036e16ada95389bdc30f41068af04c1d0872fad0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74443
Analysis date: Sat, 15 Aug 2026 16:03:05 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A vmwgfx DMA command size validation bug allows an undersized command to underflow the suffix pointer into a previous verified command, letting later verifier writes corrupt authenticated GPU command fields and potentially causing DoS or broader DRM command-stream integrity impact.

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

The original Linux kernel CVE announcement for CVE-2026-74443 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74443

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-2026-74443	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:H/I:H/A:H';CWE-124;*CWE-787;CWE-367;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A command validation bypass in drm/vmwgfx occurs because vmw_cmd_dma calculates the SVGA_3D_CMD_SURFACE_DMA suffix pointer from header size without first proving that the command body is large enough to contain the suffix. An undersized command can make the suffix pointer underflow into a previous command in the bounce buffer, and the verifier later writes suffix maximumOffset into already verified command data. This creates a TOCTOU condition on the device visible command stream and can let one command rewrite another command GMR id, surface id, or other authenticated fields. For the CVSS the PR:L is used because a local process with access to the vmwgfx DRM device or render node can submit execbuf commands without full administrator privileges in typical desktop or virtual machine deployments. The issue is not directly network reachable. Impact is at least local denial of service and authenticated command stream integrity bypass. Because the primitive is an out of bounds underwrite into validated command data, confidentiality and integrity impact are plausible and manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)	YES	OOB SIMPLEFIX DMAorINTERRUPT HARDWARE LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **8**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local unprivileged trigger: +1**. A local process with access to the vmwgfx DRM device or render node can submit execbuf commands in typical VMware desktop or guest deployments.
* **Constrained kernel buffer overwrite: +1**. The suffix pointer can underflow into a previous command in the bounce buffer, and the verifier writes `suffix->maximumOffset` there.
* **Weak LPE concern: +1**. The overwrite affects already verified command fields such as GMR id or surface id, creating a command validation bypass, but the patch does not prove arbitrary kernel write or reliable object takeover.
* **Reliable kernel crash / strong DoS: +1**. Corrupting device-visible command stream fields can realistically crash or hang the driver/device path.
* **Integrity impact plausible: +1**. The bug can rewrite authenticated command fields after validation.
* **Privileged kernel/device-management corruption path: +1**. The corruption occurs in a trusted DRM/GPU command submission path and affects validated device command metadata.

Paranoid additions / interpretation:

* **Memory corruption, strong corruption primitive instead of constrained overwrite: +1 net increase**. In the paranoid view, this is treated as an OOB underwrite into attacker-shaped command-buffer data, not merely bookkeeping.
* **Confidentiality impact plausible: +1**. Rewriting GMR or surface identifiers may plausibly redirect GPU access to resources not intended for the submitted command, although this is not demonstrated.

No remote/network signal is applied. No full admin/root penalty is applied because DRM render-node access is commonly available to non-root local users.

## 3. Reachability analysis

The bug is locally reachable through vmwgfx command submission. It is not directly network-triggerable. The most relevant attacker is a local user or process inside a VMware guest with access to the vmwgfx DRM node.

Namespaces and containers reduce reachability unless the vmwgfx device is passed through or exposed. If a container or sandbox has access to the DRM device, PR remains effectively local-low rather than full host-root.

The path is deployment-specific, but not obscure in VMware graphical guests. Realistic exploitation requires crafting an undersized `SVGA_3D_CMD_SURFACE_DMA` command so that the computed suffix pointer lands in a previous command in the bounce buffer.

Call-site confidence: **high**, because the patch and commit message describe the affected function, the pointer arithmetic, the verifier write, and the corrupted prior command fields.

## 4. Severity interpretation

This is stronger than an ordinary Moderate validation bug because the invalid size check prevents a concrete underflow write into already verified command data. Realistic demonstrated impact is command-stream integrity bypass and likely DoS. Theoretical impact may include broader confidentiality or privilege-boundary consequences inside the GPU/DRM resource model, but arbitrary kernel code execution is not proven by the patch.

Conservative handling: **Actionable Moderate**.
Paranoid handling: **Strong Important candidate** due to OOB underwrite plus authenticated command-field rewrite.

## 5. One-sentence report phrase

A vmwgfx DMA command size validation bug allows an undersized command to underflow the suffix pointer into a previous verified command, letting later verifier writes corrupt authenticated GPU command fields and potentially causing DoS or broader DRM command-stream integrity impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the patch fixes a concrete OOB underwrite / TOCTOU validation bypass in a DRM ioctl command path, with explicit corruption of authenticated command fields rather than a simple warning or DoS-only cleanup.

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

Patch: drm/vmwgfx: bound DMA command body size against suffix pointer
Commit: 036e16ada95389bdc30f41068af04c1d0872fad0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=036e16ada95389bdc30f41068af04c1d0872fad0

Commit description:

vmw_cmd_dma() locates the DMA suffix at

	(unsigned long) &cmd->body + header->size - sizeof(*suffix)

without checking that header->size is large enough to contain both
cmd->body and the suffix.  An undersized header makes the suffix
pointer underflow back into the previous command in the bounce
buffer.  The verifier later writes suffix->maximumOffset, clobbering
verified fields of an already-relocated earlier command -- a TOCTOU
on the device-visible command stream that lets one command rewrite
another's GMR id, surface id, or other authenticated fields.

Reject the command if the body is too small for the suffix to fit.

Fixes: 4e4ddd4 ("drm/vmwgfx: Fix queries if no dma buffer thrashing is occuring.")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.7
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Reviewed-by: Ian Forbes <ian.forbes@broadcom.com>
Link: https://patch.msgid.link/20260505222728.519626-8-zack.rusin@broadcom.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.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=036e16ada95389bdc30f41068af04c1d0872fad0

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

The original Linux kernel CVE announcement for CVE-2026-74443 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74443

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:H/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: 8

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).