[CVE-2026-93261][MODERATE REGULAR] locking/lockdep: Fix NULL pointer dereference in __lock_set_class() [ Upstream

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

CVE: CVE-2026-93261
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: locking/lockdep: Fix NULL pointer dereference in __lock_set_class() [ Upstream
Commit: f6093ff67ea6e347574819ed23e96e0f82a25ffc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6093ff67ea6e347574819ed23e96e0f82a25ffc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93261
Analysis date: Thu, 24 Sep 2026 14:56:08 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93261 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93261

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-93261	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93261 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';**CWE-476;CWE-125;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A lockdep NULL pointer and out of bounds dereference can occur when register_lock_class returns NULL and __lock_set_class converts the NULL result into an invalid class index. A later reacquire_held_locks operation can use this corrupted index through hlock_class and trigger a kernel warning oops or crash. For the CVSS the PR:L value is used because practical triggering requires local code execution or controlled local workload that reaches lockdep class registration and a subsequent lock reacquire path. The issue is not directly network reachable. Impact is primarily local denial of service. The paranoid score allows limited confidentiality impact because an out of bounds pointer dereference may read invalid kernel memory, but the patch does not show an information disclosure primitive or a write primitive. Lockdep is commonly enabled for debug and development kernels and is often disabled in production kernel configurations.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	WRITE OOB LOCK NULLPTR SIMPLEFIX LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

The conservative and paranoid scores are identical because the patch establishes an invalid class index and a subsequent NULL or out of bounds dereference, but does not establish disclosure, controlled reuse, an attacker controlled write, or a post fault primitive.

2. Signal breakdown

* +1 Weak indirect corruption candidate. A NULL return from register_lock_class is converted into an invalid hlock class_idx value through pointer subtraction. The corrupted index is later consumed by hlock_class.
* +1 Reliable kernel crash or strong DoS. The supplied commit explicitly identifies a NULL or out of bounds pointer dereference during reacquire_held_locks. An Oops or crash is a plausible result.
* -1 Rare and difficult to reach configuration. The vulnerable path belongs to lockdep, which is normally enabled through debug locking configurations such as CONFIG_PROVE_LOCKING and is commonly absent from production kernels. An attacker cannot enable the required kernel build time configuration.

Important non-awarded signals:

* No real UAF is established. No object is freed or released before later use.
* No controlled reclaim or attacker controlled replacement object is established.
* No arbitrary or directed write is established. The hlock class_idx assignment stores a malformed index, but the attacker does not control its value or target.
* No confidentiality impact is awarded. An internal out of bounds pointer dereference does not itself establish a read back or disclosure path.
* No integrity impact is awarded. The patch does not demonstrate modification of an attacker selected or security sensitive target.
* No remote reachability is established.
* No Local unprivileged trigger point is awarded. The supplied evidence does not show that an ordinary user can reliably exhaust lock classes or force graph_lock or key validation failure through the complete __lock_set_class and reacquire_held_locks sequence.
* No host administrator penalty is applied. Host admin privilege is not positively established as a requirement.
* No additional Availability point is awarded because the crash effect is already counted once.

3. Reachability analysis

The vulnerable operation is internal lockdep bookkeeping performed while changing the lock class or subclass of an already held lock. The immediate failure condition requires register_lock_class to return NULL due to lock class pool exhaustion, graph_lock failure, or failed key validation.

The supplied patch does not establish which caller can reliably reach __lock_set_class, whether an ordinary local process can create enough distinct lock classes, or whether a privileged kernel control plane operation is required. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

No namespace based capability path is shown. NamespaceScopedPrivilege is UNKNOWN. There is no network reachable interface, device input path, firmware path, or externally supplied packet path in the evidence.

A relevant prerequisite is a kernel built and booted with lockdep enabled. This is primarily a debug and development configuration and materially reduces practical production exposure. No special hardware is required. This is not a race condition.

4. Primitive and severity interpretation

The exact primitive is an invalid class index created by subtracting the lock_classes base address from a NULL class pointer. The malformed hlock class_idx is subsequently used by hlock_class during reacquire_held_locks, resulting in a NULL or out of bounds pointer dereference.

This is not an active structured object UAF, fixed stale storage issue, repeated release, refcount mutation, double free, or ownership violation. The stored invalid index is deterministic from the NULL value and does not provide attacker directed indexing or controlled object substitution.

PrimitiveClass is CLASS_C because the demonstrated behavior is invalid state followed by a crash capable dereference. The demonstrated consequence is local denial of service on a lockdep enabled kernel. A stronger consequence such as information disclosure, memory corruption with attacker controlled target selection, or privilege escalation is speculative and unsupported by the patch.

ImportantCandidate is NO because the patch does not establish meaningful exploitation leverage beyond the dereference. AutoDowngradeAllowed is YES because this is a constrained crash oriented invalid pointer path without a real UAF, controlled write, security boundary bypass, or unresolved lifetime mutation.

Likely operational severity is Low-like or ordinary Moderate. It should be checked for affected debug kernel builds, but it does not warrant Important classification from the supplied evidence.

5. One-sentence report phrase

A missing NULL check in lockdep __lock_set_class can convert a failed lock class registration into an invalid held lock class index and later cause a local kernel NULL or out of bounds pointer dereference.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether the deployed kernel enables CONFIG_PROVE_LOCKING or equivalent lockdep functionality and whether any attacker reachable local workload can reliably force register_lock_class failure and subsequent reacquire_held_locks execution.

7. Call-site confidence

Call-site confidence: medium

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

Patch: locking/lockdep: Fix NULL pointer dereference in __lock_set_class() [ Upstream
Commit: f6093ff67ea6e347574819ed23e96e0f82a25ffc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f6093ff67ea6e347574819ed23e96e0f82a25ffc

Changed files:
  kernel/locking/lockdep.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=f6093ff67ea6e347574819ed23e96e0f82a25ffc

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

The original Linux kernel CVE announcement for CVE-2026-93261 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93261

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 1

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).