[CVE-2026-63842][MODERATE REGULAR] drm/amdgpu/jpeg: set no_user_fence for JPEG v5.0.0 ring [ Upstream

[CVE-2026-63842][MODERATE REGULAR] drm/amdgpu/jpeg: set no_user_fence for JPEG v5.0.0 ring [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63842
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v5.0.0 ring [ Upstream
Commit: 3a55ff19a6ff5e046d6a4a18e36deec5d95d9a2e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a55ff19a6ff5e046d6a4a18e36deec5d95d9a2e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63842
Analysis date: Sun, 19 Jul 2026 11:42:38 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline but likely ordinary Moderate / Low-like
Manual review required: NO

Summary:
AMDGPU JPEG v5.0.0 rings incorrectly accepted command submissions with user fences despite not supporting 64 bit user fence writes, allowing a local user with DRM device access to trigger GPU disruption or reset rather than a demonstrated kernel memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-63842 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63842

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
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CVE-2026-63842	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:N/I:N/A:H';*CWE-20;CWE-754;CWE-703;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The AMDGPU JPEG v5.0.0 ring could accept command submissions with user fences even though this ring does not support 64 bit user fence writes. A local process with access to the AMDGPU DRM device could submit such a command stream and trigger an invalid or unsupported GPU operation. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to the render or card device, but not necessarily full administrator privileges in typical desktop or GPU compute deployments. The issue is not network reachable. Impact is denial of service through GPU fault, hang, reset, or disruption of graphics and GPU workloads. No direct confidentiality or integrity impact is indicated because the patch context does not show a kernel memory corruption primitive.';NO MANUAL CHECK; ,and ActionableScore result is Borderline but likely ordinary Moderate / Low-like (with actual score 3)  SKIP CVE-2026-63842 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline but likely ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process with access to the AMDGPU DRM render or card device can submit command streams. This is PR:L, not PR:H, because render device access is commonly delegated to non-root users or service accounts.
* Availability impact realistic: +1
  Unsupported user fence handling on a JPEG ring can plausibly cause command submission failure, GPU fault, hang, reset, or disruption of GPU workloads.

Paranoid additional signal:

* Reliable kernel crash / strong DoS: +1
  Counted only in the paranoid score. If the unsupported 64 bit user fence write reliably causes GPU reset or a broader graphics stack hang, the availability impact becomes more actionable.

Signals not applied:

* No generic memory corruption signal. The patch only sets `.no_user_fence = true` and does not show UAF, OOB write, type confusion, refcount misuse, arbitrary write, or stale pointer use.
* No privilege escalation signal. There is no demonstrated reclaim, overwrite target, callback control, or kernel memory corruption primitive.
* No high-control device API bonus. This is a GPU command submission validation fix, but the patch does not show attacker control over kernel object lifetime, page ownership, DMA mappings, refcounts, or callback targets.
* No network reachability. The trigger is local DRM command submission.
* Validation-only cap applies. The fix rejects an unsupported user-controlled configuration and does not describe a concrete downstream memory corruption primitive.

## 3. Reachability analysis

The bug is reachable by a local process that can submit AMDGPU command streams to the affected JPEG v5.0.0 ring. In many desktop, workstation, and GPU compute environments, DRM render node access may be available to non-root users through device permissions or group membership, so PR:L is the practical CVSS-style interpretation. Containers can matter if the GPU device node is passed through, but without device access the bug is not reachable. The path is not network-triggerable and depends on affected AMDGPU hardware with JPEG v5.0.0 support.

Call-site confidence: medium. The patch shows the ring capability flag but not the full CS validation path. The surrounding AMDGPU pattern is clear enough to infer that `.no_user_fence` causes command submissions with user fences to be rejected.

## 4. Severity interpretation

This behaves more like an ordinary Moderate or Low-like local device DoS than an Important-class vulnerability. The theoretical concern is that an unsupported fence operation could leave the GPU or driver in a bad state, but the patch does not support a memory-corruption, information-disclosure, or privilege-escalation primitive. The paranoid score reaches 3 only to account for a possible reliable GPU hang or reset on affected systems.

## 5. One-sentence report phrase

AMDGPU JPEG v5.0.0 rings incorrectly accepted command submissions with user fences despite not supporting 64 bit user fence writes, allowing a local user with DRM device access to trigger GPU disruption or reset rather than a demonstrated kernel memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed or handled as low-priority Moderate unless the product treats GPU reset as high-impact availability or exposes affected AMDGPU devices to untrusted multi-tenant workloads.

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

Patch: drm/amdgpu/jpeg: set no_user_fence for JPEG v5.0.0 ring [ Upstream
Commit: 3a55ff19a6ff5e046d6a4a18e36deec5d95d9a2e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a55ff19a6ff5e046d6a4a18e36deec5d95d9a2e

Changed files:
  drivers/gpu/drm/amd/amdgpu/jpeg_v5_0_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=3a55ff19a6ff5e046d6a4a18e36deec5d95d9a2e

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

The original Linux kernel CVE announcement for CVE-2026-63842 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63842

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:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 3

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).