[CVE-2026-68255][MODERATE 7.0] drm/virtio: bound EDID block reads to the response buffer

[CVE-2026-68255][MODERATE 7.0] drm/virtio: bound EDID block reads to the response buffer

[AL-KERNEL]

CVE: CVE-2026-68255
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/virtio: bound EDID block reads to the response buffer
Commit: 9fc2a017c5d597937e0c28b9a9669844aa796c42
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fc2a017c5d597937e0c28b9a9669844aa796c42
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68255
Analysis date: Mon, 10 Aug 2026 10:14:28 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious virtio-gpu backend can advertise inconsistent EDID size and extension data so that virtio_get_edid_block reads beyond the fixed EDID response buffer and exposes adjacent guest kernel memory through parsed EDID data.

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

The original Linux kernel CVE announcement for CVE-2026-68255 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68255

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-2026-68255	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:A/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '6.5';DESCR 'An out of bounds read in the virtio-gpu EDID path can occur because virtio_get_edid_block validates the requested offset only against the device supplied resp size and not against the fixed resp edid array. A malicious virtio-gpu backend can advertise a large EDID size and extension count so that later EDID block reads copy data past the array into the parsed EDID buffer. This can disclose adjacent guest kernel memory through EDID data exposed by the DRM stack. For the CVSS the PR:N is used for the paranoid score because the attacker controls the virtual GPU backend relative to the guest and does not need credentials inside the guest OS. The issue is not Internet reachable as normal TCP IP traffic. It is reachable through the virtual device boundary and is most relevant to hostile host, compromised hypervisor, or untrusted device backend scenarios. Impact is information disclosure only based on the patch evidence, with no demonstrated write primitive or direct privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	OOB VIRT SIMPLEFIX LEAK HARDWARE LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	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:

* Firmware-mediated external influence: +1
  The attacker influence comes through a malicious or compromised virtio-gpu backend, not ordinary TCP/IP network traffic.

* Confidentiality impact plausible: +1
  The patch and commit explicitly describe an out-of-bounds read where adjacent guest kernel memory can be copied into the parsed EDID data.

* Broad/default/common subsystem or broadly deployed exposure: +1
  virtio-gpu is a common virtual GPU device in Linux guest deployments, especially desktop, cloud, CI, and virtualized workstation environments.

Paranoid additional signal:

* Security-boundary bypass with practical sensitive-object access: +2
  In a threat model where the virtio backend is untrusted relative to the guest, this crosses the virtual device boundary and can expose guest kernel memory through EDID data. This is still an information disclosure primitive, not an arbitrary write or privilege escalation primitive.

Signals not applied:

* Remote reachable / network-triggerable: +0
  This is not directly reachable over normal network traffic.

* Generic memory corruption: +0
  The primitive is an OOB read only. The patch does not show OOB write, UAF, double free, type confusion, arbitrary write, or refcount corruption.

* Privilege escalation plausible: +0
  No LPE path is demonstrated by the patch. The impact is information disclosure only.

* Reliable kernel crash / strong DoS: +0
  The described issue is disclosure through EDID parsing, not a reliable crash.

## 3. Reachability analysis

The realistic attacker is a malicious virtio-gpu backend, compromised hypervisor component, hostile device model, or untrusted virtual device provider. A normal local user inside the guest generally cannot trigger the bug unless they can influence the virtio-gpu backend or the EDID response path.

Namespaces and containers do not meaningfully reduce the privilege requirement inside the guest because the controlling input is supplied by the virtual device backend. From the guest CVSS perspective, PR:N can be defensible for the paranoid model because the attacker does not need guest credentials. From an infrastructure perspective, controlling the backend is usually privileged host-side access.

The path is not Internet-exposed as TCP/IP traffic. It is exposed through the virtio device boundary and is relevant mainly for VM, cloud, sandbox, or confidential-computing-style threat models where device backends are not fully trusted.

## 4. Severity interpretation

This behaves like an actionable Moderate information disclosure issue. It is not an ordinary low-risk bounds cleanup because the commit identifies a concrete OOB read and a user-visible disclosure channel via parsed EDID data.

Theoretical impact is guest kernel memory disclosure. Realistic exploitation depends on whether the attacker can control the virtio-gpu backend or EDID response. There is no evidence of write corruption, privilege escalation, or reliable DoS, so it should not be treated as Important solely from the patch. However, because it crosses a virtualization device boundary and leaks kernel memory, it should not be auto-closed.

## 5. One-sentence report phrase

A malicious virtio-gpu backend can advertise inconsistent EDID size and extension data so that virtio_get_edid_block reads beyond the fixed EDID response buffer and exposes adjacent guest kernel memory through parsed EDID data.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete OOB read and kernel memory disclosure are present, and the risk depends heavily on the product threat model for virtio backends, confidential guests, and untrusted device emulation.

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

Patch: drm/virtio: bound EDID block reads to the response buffer
Commit: 9fc2a017c5d597937e0c28b9a9669844aa796c42
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fc2a017c5d597937e0c28b9a9669844aa796c42

Commit description:

virtio_get_edid_block() validates the read offset only against the
device-supplied resp->size field, never against the fixed-size resp->edid
array. The EDID block index is driven by the device-supplied extension
count, so a malicious virtio-gpu backend can advertise a large size
together with a high block count and read far past the array into adjacent
kernel memory, which is then surfaced in the parsed EDID (an out-of-bounds
read / info leak).

Also reject any read whose end exceeds the size of the edid array.
Conforming EDID responses stay within the array and are unaffected.

Fixes: b4b01b4 ("drm/virtio: add edid support")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patch.msgid.link/20260620-b4-disp-22bba7bf-v1-1-b95924cee742@proton.me
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/virtio/virtgpu_vq.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=9fc2a017c5d597937e0c28b9a9669844aa796c42

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

The original Linux kernel CVE announcement for CVE-2026-68255 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68255

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:A/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 6.5

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: 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).