[CVE-2026-68253][MODERATE 7.0] drm/i915/hdcp: check streams[] bounds before overflow [ Upstream

[CVE-2026-68253][MODERATE 7.0] drm/i915/hdcp: check streams[] bounds before overflow [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68253
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/i915/hdcp: check streams[] bounds before overflow [ Upstream
Commit: 84351f12390349ba010920fc247e1a0b12e41eb3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84351f12390349ba010920fc247e1a0b12e41eb3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68253
Analysis date: Mon, 10 Aug 2026 19:47:49 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: confirmed kernel OOB write, but with constrained trigger and constrained overwrite control.
Manual review required: YES

Summary:
An out-of-bounds write in the i915 HDCP MST stream collection path can occur because streams[] is written before validating data->k against INTEL_NUM_PIPES, allowing a local display-control attacker on suitable hardware to corrupt kernel memory and potentially cause DoS or broader impact.

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

The original Linux kernel CVE announcement for CVE-2026-68253 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68253

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
======================================================================

CVE-2026-68253	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:H/I:H/A:H';*CWE-787;CWE-129;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An out of bounds write in the i915 HDCP MST stream collection path can occur because data streams is written before checking whether data k has reached INTEL_NUM_PIPES. A local attacker who can influence DRM/KMS display state or HDCP MST stream configuration may be able to trigger the overflow when enough streams are processed. For the CVSS the PR:L is selected for the paranoid score because a full administrator is not necessarily required in practical desktop or service contexts where a local user or graphics process can drive display configuration. The issue is not network reachable and requires local access plus a suitable Intel i915 HDCP MST environment. Impact is at least local denial of service via kernel memory corruption and in worst case may allow confidentiality and integrity impact due to the kernel out of bounds write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	OOB SIMPLEFIX HARDWARE KPANIC 	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: confirmed kernel OOB write, but with constrained trigger and constrained overwrite control.

## 2. Signal breakdown

Triggered positive signals:

* Local unprivileged trigger: +1
  A local user or graphics session process may influence DRM/KMS display state in common desktop setups, depending on DRM master and logind permissions.

* Generic memory corruption: +2
  The patch explicitly fixes a write to data->streams[data->k] before checking that data->k is within INTEL_NUM_PIPES.

* Weak LPE concern: +1
  This is a real kernel OOB write, but the patch does not show attacker-controlled payload, attacker-selected target, reclaim, callback control, or type confusion.

* Availability impact realistic: +1
  Kernel memory corruption in the i915 display path can plausibly lead to crash or unstable display/kernel state.

* Broad deployed subsystem: +1
  i915 is widely deployed on Intel systems, although this specific HDCP MST path is not universal.

Triggered negative signals:

* Hard or special triggering conditions: -1
  Triggering appears to require a suitable Intel i915 HDCP MST configuration and enough active streams/connectors to exceed INTEL_NUM_PIPES.

* Corruption primitive highly constrained: -1
  The written value is derived from display/MST stream metadata, not an obvious attacker-controlled arbitrary payload.

Paranoid-only impact signals:

* Confidentiality impact plausible: +1
  Counted only in paranoid scoring because kernel OOB write can corrupt adjacent state, but no concrete disclosure primitive is shown.

* Integrity impact plausible: +1
  Counted only in paranoid scoring because kernel OOB write may corrupt kernel data, but no controlled overwrite or LPE chain is demonstrated.

## 3. Reachability analysis

The bug is local, not network reachable. The likely attacker model is a local user or local graphics process that can influence DRM/KMS display configuration, HDCP state, or MST stream topology. It does not require full host-root in all practical desktop environments, because display control can be delegated to a logged-in user session, but reliable triggering likely depends on hardware and display topology. Containers and namespaces usually do not help unless the container has access to the DRM device and display-control permissions. The affected subsystem is common on Intel graphics systems, but the exact HDCP MST path is configuration and hardware dependent.

Call-site confidence: medium. The changed function and immediate overflow site are visible, but full caller context and exact layout of adjacent overwritten fields are not provided.

## 4. Severity interpretation

This is not an ordinary low-risk validation cleanup. The patch moves a bounds check before a write because the previous code performed the overflow first, which is a concrete kernel memory corruption primitive. Realistic exploitation evidence is limited because the overwrite appears constrained and requires a specific i915 HDCP MST scenario. Conservative handling is borderline manual-review Moderate. Paranoid handling is Actionable Moderate and potentially Important-candidate because confirmed kernel OOB writes are historically easy to underestimate.

## 5. One-sentence report phrase

An out-of-bounds write in the i915 HDCP MST stream collection path can occur because streams[] is written before validating data->k against INTEL_NUM_PIPES, allowing a local display-control attacker on suitable hardware to corrupt kernel memory and potentially cause DoS or broader impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed kernel OOB write in a widely deployed GPU driver, with constrained but non-negligible local attack surface and unclear adjacent-object impact.

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

Patch: drm/i915/hdcp: check streams[] bounds before overflow [ Upstream
Commit: 84351f12390349ba010920fc247e1a0b12e41eb3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=84351f12390349ba010920fc247e1a0b12e41eb3

Changed files:
  drivers/gpu/drm/i915/display/intel_hdcp.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=84351f12390349ba010920fc247e1a0b12e41eb3

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

The original Linux kernel CVE announcement for CVE-2026-68253 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68253

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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).