[CVE-2026-68241][LOW] drm/i915/mst: limit DP MST ESI service loop

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

CVE: CVE-2026-68241
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/i915/mst: limit DP MST ESI service loop
Commit: e3bcd3bf7eeca9570b9fa0b2f8a602c7bcc6b0d0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3bcd3bf7eeca9570b9fa0b2f8a602c7bcc6b0d0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68241
Analysis date: Mon, 10 Aug 2026 13:20:19 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
An unbounded DP MST ESI service loop in i915 could allow a faulty or malicious physically attached MST sink device to keep interrupt handling active and cause display stack or CPU availability degradation.

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

The original Linux kernel CVE announcement for CVE-2026-68241 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68241

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: LOW
Manual review required: NO

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-2026-68241	LOW	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:N/I:N/A:H';*CWE-835;CWE-834;**CWE-400;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.6';DESCR 'An unbounded service loop in intel_dp_check_mst_status can keep processing DP MST ESI interrupts generated by a sink device without a fixed upper limit. A faulty or malicious DP MST monitor dock or hub could keep the ESI state active and make the i915 display interrupt handling path spend excessive time in the loop. For the CVSS the PR:N because no host privileges are needed once the attacker controls a physically attached DP MST sink or equivalent hardware endpoint. The issue is not network reachable and requires physical or hardware level access to the display path. Impact is denial of service only through display stack stall CPU soft lockup or degraded system responsiveness. No memory corruption information disclosure or privilege escalation primitive is visible from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	SIMPLEFIX HARDWARE 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: **1**
* Paranoid score: **2**
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* **Firmware-mediated external influence: +1**
  The trigger comes from an external DP MST sink device, such as a monitor, dock, or MST hub, which can keep ESI interrupt state active.

* **Reliable kernel crash / strong DoS: +1**
  The commit describes an unbounded service loop that may get stuck on a sink device and cause excessive interrupt processing or soft-lockup-like behavior.

* **Broad/default/common subsystem exposure: +1**
  i915 display support is broadly deployed on Intel systems, and DP MST handling is part of the normal display stack when MST hardware is used.

* **Physical-only or rare hardware-only condition: -2**
  The attacker needs control over a physically attached or hardware-level DP MST sink path. This is not reachable through a network protocol or ordinary local syscall interface.

Conservative total: **1**

Paranoid adjustment:

* **Availability impact realistic: +1**
  In the worst defensible case, a stuck display interrupt handling path could cause high availability impact, such as display stack stall, CPU soft lockup, or degraded host responsiveness.

Paranoid total: **2**

No signals for memory corruption, UAF, OOB write, privilege escalation, information disclosure, or integrity impact are supported by the patch.

## 3. Reachability analysis

The issue can be triggered by a faulty or malicious DP MST sink device that keeps generating ESI interrupt conditions. No host privileges are required once the attacker controls the physical sink device, so the practical CVSS-style PR is **PR:N**, but the attack vector is physical or hardware-mediated rather than local software or network.

Namespaces and containers do not materially affect reachability because the vulnerable path is in the host display driver and is driven by DisplayPort MST hardware behavior, not by a namespaced userspace API.

The affected code is enabled in normal i915 DP MST support, but exploitation requires a relevant Intel display environment and a connected MST-capable sink, dock, or hub. This makes the bug real but narrow in exposure.

## 4. Severity interpretation

This behaves like a **Low-like / ordinary Moderate availability issue**, not an Important-class vulnerability. The patch only bounds an otherwise unbounded interrupt service loop. There is no visible memory lifetime issue, no stale pointer, no overwrite, no page-cache or ownership violation, and no privilege-escalation primitive.

The theoretical worst case is a stronger DoS if the display stack or CPU gets stuck servicing sink-originated interrupts. Realistic exploitation evidence supports availability impact only.

## 5. One-sentence report phrase

An unbounded DP MST ESI service loop in i915 could allow a faulty or malicious physically attached MST sink device to keep interrupt handling active and cause display stack or CPU availability degradation.

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

This is a physical or hardware-mediated DoS-only issue with no supported memory corruption, privilege escalation, confidentiality, or integrity primitive.

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

Patch: drm/i915/mst: limit DP MST ESI service loop
Commit: e3bcd3bf7eeca9570b9fa0b2f8a602c7bcc6b0d0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3bcd3bf7eeca9570b9fa0b2f8a602c7bcc6b0d0

Commit description:

The loop in intel_dp_check_mst_status() keeps servicing interrupts
originating from the sink without bound. Add an upper bound to the new
interrupts occurring during interrupt processing to not get stuck on
potentially stuck sink devices. Use arbitrary 32 tries to clear incoming
interrupts in one go.

Discovered using AI-assisted static analysis confirmed by Intel Product
Security.

Note: The condition likely pre-dates the commit in the Fixes: tag, but
this is about as far back as a backport has any chance of
succeeding. Before that, the retry had a goto.

Reported-by: Martin Hodo <martin.hodo@intel.com>
Fixes: 3c0ec2c ("drm/i915: Flatten intel_dp_check_mst_status() a bit")
Cc: stable@vger.kernel.org # v5.8+
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260625142204.1078287-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit b4ea527 )
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/i915/display/intel_dp.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=e3bcd3bf7eeca9570b9fa0b2f8a602c7bcc6b0d0

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

The original Linux kernel CVE announcement for CVE-2026-68241 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68241

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.6

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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).