[CVE-2026-53137][MODERATE 7.0] drm/amd/display: Clamp HDMI HDCP2 rx_id_list read to buffer size

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

CVE: CVE-2026-53137
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/amd/display: Clamp HDMI HDCP2 rx_id_list read to buffer size
Commit: 3c4444aec06c74fbc05661f370954ac814963c38
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c4444aec06c74fbc05661f370954ac814963c38
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53137
Analysis date: Fri, 31 Jul 2026 16:32:26 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious HDMI HDCP 2.x repeater or sink can advertise an oversized ReceiverID-list length and cause an out-of-bounds write into the AMD display driver rx_id_list buffer during DDC/I2C reads, making this a physical peripheral-triggered kernel memory corruption issue requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53137 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53137

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-2026-53137	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-119;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'During HDMI HDCP 2.x repeater authentication, the AMD display driver used the repeater supplied ReceiverID list size as the I2C read length without clamping it to the rx_id_list buffer size. A malicious HDMI repeater or sink can advertise a size larger than rx_id_list and cause an out-of-bounds write in kernel memory during the DDC read. For the CVSS the PR:N is used because the attacker does not need an account or privileges on the victim system, only the ability to present a malicious HDMI device to the target. The issue is not network reachable in the IP sense and is best modeled as a physical peripheral attack. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the primitive is a device-controlled OOB write into kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-53137  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB SIMPLEFIX HARDWARE KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Firmware/peripheral-mediated external influence: +1. The attacker influence comes from a malicious HDMI repeater or sink over DDC/I2C during HDCP 2.x authentication.
* Constrained kernel buffer overwrite: +1. The bug is an OOB write into a kernel driver buffer, but the destination is a specific rx_id_list buffer and adjacent overwrite target control is not shown.
* Confidentiality impact plausible: +1. Kernel memory corruption can plausibly affect sensitive state, but no direct leak primitive is shown.
* Integrity impact plausible: +1. The write crosses the intended buffer boundary in kernel memory.
* Availability impact realistic: +1. OOB writes in a display driver can realistically crash or destabilize the kernel.
* Privileged kernel/device-management corruption path: +1. The corruption occurs in a trusted DRM/AMD display HDCP path using device supplied data.
* Physical-only condition: -2. The attacker needs physical or equivalent HDMI device control, not IP network reachability.

Paranoid additions/changes:

* Memory corruption, strong corruption primitive: +2 instead of constrained +1. In the worst still-defensible interpretation, a malicious HDMI device controls both the advertised length and returned ReceiverID-list bytes, producing a device-controlled OOB write in kernel memory.
* Weak to moderate LPE concern: +1. Privilege escalation is not demonstrated, but kernel OOB write from attacker-controlled peripheral data is enough to require manual review.

## 3. Reachability analysis

The realistic attacker is a person or device able to connect or emulate a malicious HDMI repeater or sink to the affected AMD display output. No local account on the victim is required, so PR:N is reasonable for CVSS-style reasoning, but the attack is physical/peripheral-mediated rather than network reachable. Containers and namespaces do not materially affect reachability because the trigger is outside the local userspace permission model. The path requires HDMI HDCP 2.x repeater authentication, so exposure depends on display hardware, HDCP use, and whether a malicious repeater/sink can participate.

## 4. Severity interpretation

This is more than an ordinary Moderate correctness issue because the patch fixes a concrete OOB write into kernel memory. It is not a strong Important candidate by default because exploitation requires malicious physical/peripheral access and the overwrite target is not shown to be reliably selectable. The realistic impact is crash or kernel memory corruption during HDMI HDCP authentication. The theoretical worst case includes confidentiality or integrity impact, but practical LPE evidence is not demonstrated.

## 5. One-sentence report phrase

A malicious HDMI HDCP 2.x repeater or sink can advertise an oversized ReceiverID-list length and cause an out-of-bounds write into the AMD display driver rx_id_list buffer during DDC/I2C reads, making this a physical peripheral-triggered kernel memory corruption issue requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a device-controlled OOB write in kernel memory. The physical-only reachability lowers practical exposure, but the primitive is strong enough to require human review of structure layout, overwrite controllability, and crash or LPE feasibility.

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UPSTREAM PATCH SUMMARY
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Patch: drm/amd/display: Clamp HDMI HDCP2 rx_id_list read to buffer size
Commit: 3c4444aec06c74fbc05661f370954ac814963c38
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c4444aec06c74fbc05661f370954ac814963c38

Commit description:

[Why & How]
During HDCP 2.x repeater authentication over HDMI, the driver reads the
sink's RxStatus register and extracts a 10-bit message size field (max
value 1023). This value is used as the read length for the ReceiverID
list without being clamped to the size of the destination buffer
rx_id_list[177]. A malicious HDMI repeater could advertise a message
size larger than the buffer, causing an out-of-bounds write during the
I2C read.

Clamp the read length in mod_hdcp_read_rx_id_list() to the size of the
rx_id_list buffer, matching the approach already used in the DP branch.

Fixes: eff682f ("drm/amd/display: Add DDC handles for HDCP2.2")
Assisted-by: Copilot:claude-opus-4.6
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 2292122 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/modules/hdcp/hdcp_ddc.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=3c4444aec06c74fbc05661f370954ac814963c38

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

The original Linux kernel CVE announcement for CVE-2026-53137 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53137

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 4
  Paranoid ActionableScore: 6

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).