[CVE-2026-46263][MODERATE REGULAR] drm/amd/display: Fix out-of-bounds stream encoder index v3 [ Upstream

[CVE-2026-46263][MODERATE REGULAR] drm/amd/display: Fix out-of-bounds stream encoder index v3 [ Upstream

[AL-KERNEL]

CVE: CVE-2026-46263
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amd/display: Fix out-of-bounds stream encoder index v3 [ Upstream
Commit: 29f3824b08a98d41ecbbfd33580630d7607f962e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29f3824b08a98d41ecbbfd33580630d7607f962e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46263
Analysis date: Sat, 01 Aug 2026 09:33:44 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / below Actionable Moderate
Manual review required: YES

Summary:
An AMD display stream encoder creation path could index `stream_enc_regs` out of bounds when `eng_id` is invalid, allowing a local DRM/KMS-triggered display driver malfunction or kernel-side DoS on affected AMD DCN hardware.

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

The original Linux kernel CVE announcement for CVE-2026-46263 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46263

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: 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
======================================================================

CVE-2026-46263	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-129;CWE-125;CWE-823;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'An out of bounds access in AMD display stream encoder creation occurs because eng_id was accepted up to ENGINE_ID_DIGF while stream_enc_regs has only 5 entries. If eng_id is 5 or negative, the code can pass an out of range stream_enc_regs entry into the encoder constructor, which may use invalid register definitions and can lead to display driver malfunction or kernel side DoS. For the CVSS the PR:L is used for the paranoid score because a local user with access to DRM KMS display configuration may be able to influence modeset paths, although reliable triggering depends on AMD DCN hardware and resource selection. The issue is not network reachable. Impact is primarily availability, with limited confidentiality or integrity impact kept for manual review sensitivity because this is an out of bounds kernel access rather than a simple resource leak.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / below Actionable Moderate (with actual score 4) 	MAYBE	WRITE OOB HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / below Actionable Moderate**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger plausible: +1
  DRM/KMS display configuration paths can be reachable by a local graphical user or DRM master, although direct control over `eng_id` is not clearly shown.

* Memory corruption, weak/indirect corruption candidate: +1
  `eng_id` is used as an unchecked array index into `stream_enc_regs[]`, producing an out-of-bounds pointer passed into the stream encoder constructor. This is an OOB access, but not an OOB write or demonstrated controlled overwrite.

* Availability impact realistic: +1
  Invalid register table selection can plausibly cause display driver malfunction, GPU/display failure, or kernel-side DoS.

Paranoid additional signal:

* Privileged kernel/device-management corruption path: +1
  The OOB access occurs inside AMD display resource construction, a trusted GPU/display driver path using hardware register definitions. This justifies manual review, but not Important classification without a stronger primitive.

Not counted:

* Remote reachable: +0
  No network path.

* Strong LPE plausibility: +0
  No attacker-controlled reclaim, arbitrary write, callback control, type confusion, or refcount abuse is shown.

* Confidentiality / Integrity: +0 conservative
  The patch shows OOB read/use of a register descriptor entry, but no user-visible disclosure or attacker-controlled write primitive.

* Rare hardware-only penalty: 0
  AMD DCN display paths are hardware-specific, but not rare enough to heavily penalize in triage.

Call-site confidence: medium. The immediate indexed use and constructor call are visible, but broader caller control over `eng_id` is not fully shown.

## 3. Reachability analysis

A local user with access to DRM/KMS modesetting paths may be able to reach stream encoder creation during display configuration changes. In typical desktop systems, this may be available to the active graphical user through DRM device permissions, while on servers or locked-down systems it may require privileged display management access. Containers usually do not get direct DRM/KMS control unless the GPU device is delegated. The path is not network reachable and depends on AMD DCN hardware plus resource selection that can produce `ENGINE_ID_DIGF` or an invalid `eng_id`.

## 4. Severity interpretation

This behaves like a weak kernel OOB access with plausible local DoS, not a demonstrated Important-class vulnerability. Theoretical memory-corruption concern exists because an out-of-range kernel array entry is used as a structure pointer source, but the patch does not show an OOB write, attacker-controlled payload, stale object reuse, or privilege-escalation primitive. The practical evidence supports Borderline / manual review rather than auto-close, but does not reach Actionable Moderate under this scoring formula.

## 5. One-sentence report phrase

An AMD display stream encoder creation path could index `stream_enc_regs` out of bounds when `eng_id` is invalid, allowing a local DRM/KMS-triggered display driver malfunction or kernel-side DoS on affected AMD DCN hardware.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is kernel OOB access in a GPU driver resource construction path, but current evidence shows only weak/indirect corruption and likely DoS rather than a concrete privilege-escalation primitive.

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

Patch: drm/amd/display: Fix out-of-bounds stream encoder index v3 [ Upstream
Commit: 29f3824b08a98d41ecbbfd33580630d7607f962e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=29f3824b08a98d41ecbbfd33580630d7607f962e

Changed files:
  drivers/gpu/drm/amd/amdgpu/../display/dc/resource/dcn351/dcn351_resource.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=29f3824b08a98d41ecbbfd33580630d7607f962e

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

The original Linux kernel CVE announcement for CVE-2026-46263 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46263

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:H/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 4

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).