[CVE-2026-98181][MODERATE REGULAR] drm/gud: fix out-of-bounds write in gud_plane_atomic_check()

[CVE-2026-98181][MODERATE REGULAR] drm/gud: fix out-of-bounds write in gud_plane_atomic_check()

[AL-KERNEL]

CVE: CVE-2026-98181
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/gud: fix out-of-bounds write in gud_plane_atomic_check()
Commit: ee04903fe6a098160d20dde4fc5af4cb42846735
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee04903fe6a098160d20dde4fc5af4cb42846735
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98181
Analysis date: Thu, 08 Oct 2026 09:38:55 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98181 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98181

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.

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

CVE-2026-98181	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98181 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (legacy and Aegis reconciliation differ; DECISION: legacy MODERATE vs Aegis MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-122;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'An out of bounds kernel write in the DRM GUD USB display driver occurs because gud_plane_atomic_check uses num_properties plus i as the property array index while num_properties is also incremented in the same loop. A malicious USB display device can advertise enough connector and plane properties to make the driver write past the end of the allocated request property array. For the CVSS the PR:N because the attacker does not need an account or privileges on the target system but must connect or control a malicious physical USB device. The attack vector is AV:P and is not network reachable in the normal deployment model. The base impact is local denial of service or limited memory corruption. The paranoid impact includes potential confidentiality integrity and availability compromise because this is a kernel heap out of bounds write and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	WRITE OOB SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +1 Constrained kernel buffer overwrite. The patch fixes a concrete write beyond the allocated req properties array. The demonstrated overwrite is bounded to at least one property slot beyond the end of the allocation.
* +1 Firmware mediated external influence. A malicious USB GUD display device can advertise the maximum property count needed to reach the faulty index calculation.
* +1 Reliable kernel crash or strong DoS concern. A kernel heap out of bounds write can corrupt adjacent allocation state and can realistically result in a kernel fault or crash. A deterministic panic is not demonstrated by the supplied patch.
* +1 Paranoid only. The affected write is a structured property and value write into memory adjacent to a kernel allocation. The precise adjacent object and write contents require manual analysis, but the primitive is more serious than a read only bounds violation.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated. The patch establishes an out of bounds write but does not establish attacker selection of the adjacent allocation target.
* Strong LPE plausibility is not separately awarded. A complete object replacement, callback, credential, refcount takeover, or arbitrary read write primitive is not shown.
* Confidentiality and integrity consequences are not independently awarded. The existence of an out of bounds write alone does not prove disclosure or modification of security sensitive objects.
* Remote reachability is not established. The supplied trigger requires a malicious or attacker controlled USB display device.
* No physical only or rare hardware penalty is applied. USB display hardware is device specific, but USB access and USB display devices are not inherently rare hardware. Physical device access remains a material practical restriction.
* Extra Availability impact is not awarded because the possible kernel crash is already counted as the DoS signal.

3. Reachability analysis

The trigger is a malicious USB device implementing the GUD USB display protocol and advertising sufficient connector and plane properties. The vulnerable path is in DRM atomic plane validation, so the device must be bound to the GUD driver and a relevant DRM atomic configuration path must be exercised.

A local logged in user, compositor, display server, DRM master, delegated graphics service, or host administrator may cause atomic display operations after device attachment. However, the supplied context does not establish which of these actors can perform the complete trigger sequence on a particular distribution or desktop configuration.

HostAdminRequired is UNKNOWN. The patch does not show that host root is required, but it also does not prove that an ordinary desktop user can independently drive the full KMS atomic operation after attaching the malicious device.

NamespaceScopedPrivilege is UNKNOWN. DRM and physical USB device attachment are not shown to be fully controllable through attacker reachable user or network namespaces. No network trigger is established. No boot parameter, sysctl, or special non default hardware prerequisite is established beyond CONFIG_DRM_GUD and attachment of a GUD compatible USB display device.

4. Primitive and severity interpretation

The exact primitive is a bounded kernel heap out of bounds write in gud_plane_atomic_check. The loop uses num_properties plus i as an index while num_properties is incremented during each iteration. This advances the write index by two property slots per iteration instead of one. With two connector properties and thirty two plane properties, the final write reaches index 64 for a sixty four element allocation.

This is not a UAF and does not involve a repeated release or refcount mutation. It is not fixed stale storage or cleanup only behavior. It is a direct bounds violation during active DRM request construction.

The write is currently best classified as constrained CLASS_B kernel corruption. The patch proves that a USB controlled property count reaches an out of bounds write, but it does not prove useful control over the adjacent allocation target, controlled reclaim, active object replacement, a callback overwrite, arbitrary kernel read write, information disclosure, or privilege escalation.

The demonstrated consequence is kernel memory corruption with plausible kernel crash or denial of service. A stronger consequence such as privilege escalation remains speculative until the allocation layout, property value origin, overwrite width, and adjacent object use are manually reviewed.

ImportantCandidate is YES because this is a concrete attacker triggered kernel heap write, not a validation warning or a crash only invalid pointer dereference. AutoDowngradeAllowed is NO because automatically closing the issue as an ordinary driver bug would discard an unresolved kernel memory corruption primitive.

Likely operational severity is constrained by physical USB access and the requirement that the GUD driver and DRM atomic path are active. Nevertheless, the bug should receive manual review because a one slot out of bounds kernel write can have materially different impact depending on allocator layout and the adjacent object.

5. One-sentence report phrase

A malicious USB GUD display device can trigger a bounded kernel heap out of bounds write in gud_plane_atomic_check by advertising enough properties to advance the property array index past its allocation, requiring manual analysis for possible corruption beyond denial of service.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Concrete USB triggered kernel heap out of bounds write is established, while overwrite contents, adjacent allocation layout, and practical exploitation leverage are unresolved.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/gud: fix out-of-bounds write in gud_plane_atomic_check()
Commit: ee04903fe6a098160d20dde4fc5af4cb42846735
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee04903fe6a098160d20dde4fc5af4cb42846735

Commit description:

The plane property loop uses req->properties[num_properties + i] as write
index while simultaneously incrementing `num_properties` inside the loop.
At iteration i, num_properties has also incremented by i, so the write
is done at `initial_num_properties + 2*i`, skipping every other index and
advancing by 2 per iteration.

With just 2 connector and 32 plane properties the last write happens at
index 64, one slot past the end of the 64-slot (indices 0–63)
allocation. A USB device can trigger OOB by advertising the maximum
number of properties.

Fix by dropping the redundant `+ i`; num_properties is already the correct
running index, as gud_connector_fill_properties() fills the preceding
slots.

Fixes: 40e1a70 ("drm: Add GUD USB Display driver")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260821071812.16500-1-sajal2005gupta%40gmail.com?part=1
Signed-off-by: Sajal Gupta <sajal2005gupta@gmail.com>
Cc: <stable@vger.kernel.org>
Acked-by: Ruben Wauters <rubenru09@aol.com>
Signed-off-by: Ruben Wauters <rubenru09@aol.com>
Link: https://patch.msgid.link/20260902123254.36987-1-sajal2005gupta@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/gud/gud_pipe.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=ee04903fe6a098160d20dde4fc5af4cb42846735

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

The original Linux kernel CVE announcement for CVE-2026-98181 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98181

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 4

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).