[CVE-2026-64524][MODERATE REGULAR] drm/hyperv: validate resolution_count and fix WIN8 fallback [ Upstream

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

CVE: CVE-2026-64524
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/hyperv: validate resolution_count and fix WIN8 fallback [ Upstream
Commit: 96f7de3172d4aa878b7f87173b2b3507c350fcd6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96f7de3172d4aa878b7f87173b2b3507c350fcd6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64524
Analysis date: Sat, 25 Jul 2026 07:48:43 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A malformed Hyper-V synthetic video resolution response can make the Linux guest DRM driver read past the supported resolution array and may also leave framebuffer limits unset, causing guest display denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-64524 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64524

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
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CVE-2026-64524	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:H/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-129;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.6';DESCR 'Hyper-V synthetic video can accept a SYNTHVID_RESOLUTION_RESPONSE with resolution_count larger than the supported_resolution array and then parse past the fixed 64 entry array. This is an out of bounds read in the guest DRM driver controlled by the Hyper-V host or VSP side, and it can also leave screen limits unset so framebuffer creation fails with EINVAL. For the CVSS the PR:H is used because reliable triggering normally requires control of the Hyper-V host or synthetic video service rather than an ordinary guest user. The issue is not network reachable from outside the VM and is triggered through the Hyper-V synthetic video channel. Impact is mainly guest display denial of service, with limited confidentiality or integrity impact kept only for the paranoid score because the primitive is an out of bounds read and not an out of bounds write or UAF.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

* Firmware-mediated external influence: +1
  The malformed SYNTHVID_RESOLUTION_RESPONSE is supplied through the Hyper-V synthetic video channel by the host or VSP side, not by ordinary guest userspace.

* Availability impact realistic: +1
  The WIN10 probe failure path can leave screen limits unset, causing framebuffer creation to fail with -EINVAL. This is a practical guest display DoS, but not a general host-wide kernel crash.

* Privileged kernel/device-management path, paranoid only: +1
  The OOB read occurs in a guest kernel DRM driver while parsing host-provided synthetic device data. This deserves manual review, but the primitive is read-only and driver-local.

* Weak corruption / limited OOB read: +0
  The patch shows an array over-read past supported_resolution[64], but no OOB write, UAF, double-free, stale callback, refcount abuse, or attacker-controlled object replacement.

* Remote reachable / network-triggerable: +0
  This is not reachable over the network from outside the VM.

* Privilege escalation plausible: +0
  No LPE path is shown. The bug is host-to-guest device input handling, not a guest local user to guest root path.

* Confidentiality / integrity impact: +0 conservative
  There is no demonstrated disclosure channel or write primitive. Limited C:L/I:L may be kept only in CVSS paranoid triage, but the actionable score should not treat this as strong corruption.

## 3. Reachability analysis

The realistic trigger is a malicious, compromised, or faulty Hyper-V host or synthetic video service returning resolution_count greater than SYNTHVID_MAX_RESOLUTION_COUNT. Ordinary guest users generally cannot trigger this directly unless they can influence the Hyper-V VSP side. Containers and namespaces inside the guest do not materially lower privileges because the vulnerable input comes from the virtual device channel, not from a local guest API. The path is relevant only for Linux guests using the Hyper-V DRM synthetic video driver.

## 4. Severity interpretation

This behaves more like a borderline Moderate issue than an Important-class vulnerability. The theoretical concern is a host-controlled OOB read in guest kernel code, which warrants manual review. The realistic demonstrated impact is guest display DoS or framebuffer creation failure, with no concrete evidence of UAF, OOB write, arbitrary write, credential impact, or guest privilege escalation.

## 5. One-sentence report phrase

A malformed Hyper-V synthetic video resolution response can make the Linux guest DRM driver read past the supported resolution array and may also leave framebuffer limits unset, causing guest display denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The issue is not Important by default, but manual review is justified because host-controlled device data reaches an OOB read in guest kernel code.

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

Patch: drm/hyperv: validate resolution_count and fix WIN8 fallback [ Upstream
Commit: 96f7de3172d4aa878b7f87173b2b3507c350fcd6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96f7de3172d4aa878b7f87173b2b3507c350fcd6

Changed files:
  drivers/gpu/drm/hyperv/hyperv_drm_proto.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=96f7de3172d4aa878b7f87173b2b3507c350fcd6

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

The original Linux kernel CVE announcement for CVE-2026-64524 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64524

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:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.6

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: 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).