[CVE-2026-53138][MODERATE 7.0] drm/amd/display: Bound VBIOS record-chain walk loops

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

CVE: CVE-2026-53138
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amd/display: Bound VBIOS record-chain walk loops
Commit: 6173cfea2f916e01c4f98e29cd654384a05e32a3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6173cfea2f916e01c4f98e29cd654384a05e32a3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53138
Analysis date: Fri, 31 Jul 2026 16:27:40 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
Malformed AMD display VBIOS record chains can cause unbounded BIOS parser loops during GPU probe and may also trigger limited out-of-bounds reads near the firmware image boundary, leading primarily to local or firmware-mediated denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-53138 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53138

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-2026-53138	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-835;CWE-125;*CWE-20;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'Malformed AMD display VBIOS record chains without a 0xFF terminator or zero record size can make the BIOS parser walk records for an unbounded number of iterations during GPU probe. This can cause high CPU usage or a probe time denial of service, and near the VBIOS image boundary the parser may also perform out of bounds reads after validating only the small record header. For the CVSS the PR:L is used in the paranoid score because some deployments may expose GPU reprobe, reset, firmware override, or device assignment flows to a reduced privilege local user or service account. The issue is not network reachable and normally requires local administrative control over the VBIOS image or a malicious device. Impact is primarily denial of service, with limited confidentiality or integrity impact considered only for the paranoid score due to the out of bounds read primitive. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) 	MAYBE	OOB DANGER SIMPLEFIX HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* +1 Firmware-mediated external influence: the parser consumes VBIOS data supplied by firmware or device-specific firmware paths.
* +1 Reliable kernel crash / strong DoS: malformed record chains can cause unbounded probe-time iteration and effectively hang or stall GPU initialization.
* +1 Availability impact realistic: the issue occurs during probe and can persist until the malformed VBIOS or device condition is removed.
* +1 Broad/default/common subsystem: AMDGPU display support is broadly deployed on systems with AMD GPUs.
* -1 Special precondition: practical triggering usually requires malformed VBIOS control, firmware override, malicious device, or similar non-default influence.

Paranoid additional signals:

* +1 Local reduced-privilege trigger concern: some environments may expose GPU reset, reprobe, passthrough, or device-management flows to service accounts, container-adjacent users, or reduced-capability administrators rather than full host root.
* +1 Weak/indirect corruption candidate: the commit explicitly states that near the BIOS image boundary, struct casts beyond the 2-byte header validated by GET_IMAGE can read out of bounds. This is not a strong corruption primitive, but it is more than a pure infinite-loop bug.

Not counted:

* No remote/network trigger.
* No strong LPE signal.
* No OOB write, UAF, double-free, type confusion, arbitrary write, callback control, or page-cache corruption.
* No confirmed confidentiality disclosure path from the limited OOB read.

## 3. Reachability analysis

The realistic trigger is a malformed AMD VBIOS image missing the expected 0xFF terminator or zero record_size sentinel. In normal deployments, modifying or supplying such firmware usually requires administrator control, firmware override, a malicious or compromised device, or a hardware/virtualization setup where the device firmware image is attacker influenced.

This is not network reachable. Namespaces do not normally make VBIOS modification unprivileged. However, GPU reset, reprobe, passthrough, or device-management workflows may be delegated in some environments, which supports the paranoid PR:L-style interpretation.

Call-site confidence: high. The affected loops and parser call context are shown directly in the patch.

## 4. Severity interpretation

This behaves primarily like an actionable Moderate firmware-parser DoS. The strongest realistic impact is probe-time hang or kernel-side stall caused by unbounded record-chain walking.

The theoretical memory-safety concern is limited OOB read from malformed firmware data near the BIOS image boundary. That justifies manual review and the paranoid score, but the patch does not show an attacker-controlled write, reclaim primitive, privilege escalation path, or direct information disclosure channel. Therefore it should not be treated as a strong Important memory-corruption candidate based on the provided evidence alone.

## 5. One-sentence report phrase

Malformed AMD display VBIOS record chains can cause unbounded BIOS parser loops during GPU probe and may also trigger limited out-of-bounds reads near the firmware image boundary, leading primarily to local or firmware-mediated denial of service.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is not merely resource exhaustion because the commit explicitly mentions out-of-bounds reads after only the small record header was validated. The current evidence supports Actionable Moderate handling, but not a strong LPE or Important classification without additional proof of disclosure, write corruption, or controllable memory misuse.

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

Patch: drm/amd/display: Bound VBIOS record-chain walk loops
Commit: 6173cfea2f916e01c4f98e29cd654384a05e32a3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6173cfea2f916e01c4f98e29cd654384a05e32a3

Commit description:

[Why & How]
All record-chain walk loops in bios_parser.c and bios_parser2.c use
for(;;) and only terminate on a 0xFF record_type sentinel or zero
record_size. A malformed VBIOS image missing the terminator record
causes unbounded iteration at probe time, potentially hundreds of
thousands of iterations with record_size=1. In the final iterations
near the BIOS image boundary, struct casts beyond the 2-byte header
validated by GET_IMAGE can also read out of bounds.

Cap all 14 record-chain walk loops to BIOS_MAX_NUM_RECORD (256)
iterations. The atombios.h defines up to 22 distinct record types
and atomfirmware.h has 13. Assuming an average of less than 10
records per type (which is reasonable since most are connector-
based) 256 is a generous upper bound.

Fixes: 4562236 ("drm/amd/dc: Add dc display driver (v2)")
Assisted-by: Copilot:claude-opus-4.6 Mythos
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 95700a3 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/dc/bios/bios_parser.c
  drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
  drivers/gpu/drm/amd/display/dc/bios/bios_parser_helper.h

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=6173cfea2f916e01c4f98e29cd654384a05e32a3

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

The original Linux kernel CVE announcement for CVE-2026-53138 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53138

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:H/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: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: 3
  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: NO
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).