[CVE-2025-71305][LOW] drm/display/dp_mst: Add protection against 0 vcpi [ Upstream

[CVE-2025-71305][LOW] drm/display/dp_mst: Add protection against 0 vcpi [ Upstream

[AL-KERNEL]

CVE: CVE-2025-71305
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/display/dp_mst: Add protection against 0 vcpi [ Upstream
Commit: 95dbd525efce2a9e9e1c50ad15213de644c85ad0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95dbd525efce2a9e9e1c50ad15213de644c85ad0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-71305
Analysis date: Mon, 06 Jul 2026 19:48:12 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2025-71305 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-71305

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2025-71305	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-682;CWE-190;CWE-758;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.2';DESCR 'A shift-out-of-bounds condition in the DRM DisplayPort MST path can occur when delayed_destroy_work runs after a DP 2.1 monitor disconnect and payload vcpi becomes 0. The code then evaluates BIT(vcpi - 1), which creates a negative shift exponent and triggers UBSAN. For the CVSS the PR:N because physical hotplug triggering does not require an authenticated local user account, although it requires physical access to the display path. The issue is not network reachable and is tied to DisplayPort MST hotplug or disconnect behavior. Impact is mainly denial of service or display stack disruption, with higher availability impact only on systems where UBSAN or warning conditions can panic the kernel.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0) 	YES	WRITE KASAN OOB LOG HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=0

1. ActionableScore
* Conservative score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Physical-only or rare hardware-only condition: -2. Trigger depends on DP MST hotplug or disconnect behavior with a DP 2.1 monitor.
* Hard or unreliable race / special timing required: -1. The issue requires delayed_destroy_work to run after disconnect while vcpi has become 0.
* Reliable kernel crash / strong DoS: +0 conservative. The provided trace shows UBSAN shift-out-of-bounds warning, not a proven unconditional kernel panic.
* Availability impact realistic: +1 only in a weak sense. The issue may disrupt the display stack or panic only on systems configured to treat UBSAN or warnings as fatal.
* Generic memory corruption: +0. Negative shift is undefined behavior and a bad mask calculation, but the patch does not show UAF, OOB write, double free, type confusion, or attacker-controlled overwrite.
* Confidentiality impact: +0. No disclosure path is shown.
* Integrity impact: +0. No write primitive or security boundary bypass is shown.

Net score is clamped to 0 because negative physical and timing constraints outweigh the weak availability signal.

3. Reachability analysis
The practical trigger is physical or local-physical interaction with a DisplayPort MST setup, especially disconnecting a DP 2.1 monitor while delayed destroy work later releases a payload whose vcpi is 0. It is not network reachable. It does not require an authenticated local user account in the CVSS sense, but it does require physical access or control over the display hotplug path. Containers and namespaces do not meaningfully improve reachability because this is a DRM hotplug and workqueue path tied to real display hardware. The path is only relevant on systems using affected DRM DP MST configurations.

4. Severity interpretation
This behaves like a Low-like or ordinary Moderate robustness bug, not an Important-class vulnerability. The demonstrated failure mode is a UBSAN negative shift warning in payload mask handling. The theoretical worst case is display disruption or kernel panic on hardened/debug configurations with panic-on-warning behavior, but the patch does not support memory corruption, privilege escalation, information disclosure, or cross-boundary access.

5. One-sentence report phrase
A DP MST delayed destroy path can evaluate BIT(vcpi - 1) after vcpi becomes 0 on monitor disconnect, causing a UBSAN negative shift warning and possible display DoS on affected physical hardware setups.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The patch shows a narrow physical hotplug-triggered arithmetic bounds issue with no demonstrated memory corruption primitive, no network exposure, and no plausible privilege escalation path.

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

Patch: drm/display/dp_mst: Add protection against 0 vcpi [ Upstream
Commit: 95dbd525efce2a9e9e1c50ad15213de644c85ad0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95dbd525efce2a9e9e1c50ad15213de644c85ad0

Changed files:
  drivers/gpu/drm/display/drm_dp_mst_topology.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=95dbd525efce2a9e9e1c50ad15213de644c85ad0

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

The original Linux kernel CVE announcement for CVE-2025-71305 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-71305

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:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.2

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: unknown
  Paranoid ActionableScore: 0

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).