[CVE-2026-97918][MODERATE REGULAR] tracing: Undo the registration when enabling the histogram trigger fails [ Upstream

[CVE-2026-97918][MODERATE REGULAR] tracing: Undo the registration when enabling the histogram trigger fails [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97918
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tracing: Undo the registration when enabling the histogram trigger fails [ Upstream
Commit: 51b07104d563d4be2be34158d3b9d922ca417642
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51b07104d563d4be2be34158d3b9d922ca417642
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97918
Analysis date: Fri, 25 Sep 2026 09:18:55 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A failed tracing histogram-trigger enable operation can leave a freed trigger referenced by the global named_triggers list, allowing a later lookup to dereference stale memory and cause a local kernel crash or denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-97918 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97918

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-2026-97918	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97918 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'A use-after-free in tracing histogram trigger cleanup occurs when enabling a trigger fails after it has been registered in the global named trigger list. The error path removes the trigger from the per file list before normal unregister processing, so cleanup cannot remove the global reference and later find_named_trigger can dereference freed memory. This can cause a kernel crash and the confirmed stale reference to freed memory creates a plausible risk of confidentiality integrity and privilege impact that requires manual review. For the CVSS the PR:H because creating or modifying histogram triggers normally requires administrative tracefs access such as CAP_SYS_ADMIN. The issue is local and is not directly network reachable. The high attack complexity reflects the need to reach the failed enable and cleanup sequence. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	READ INIT TRACE UAF IMPROVEONLY LINUS TEST 	NO	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative floor: 3 -> 4. The bug is a confirmed non-fixed-storage UAF with a stale object reachable through the global named_triggers list. Host-admin-equivalent privilege is not positively established by the supplied material.
* Applied paranoid floor: 3 -> 4. No additional paranoid point is justified because controlled reclaim, post-free attacker-controlled contents, a second lifetime mutation, disclosure, or a security-boundary bypass is not established.
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation. The trigger object is freed while its list entry remains reachable through the global named_triggers list. A later find_named_trigger traversal dereferences the freed object. The KASAN report directly confirms slab use-after-free.
* +1 Reliable kernel crash / strong DoS. The stale list entry is dereferenced in kernel tracing code. The demonstrated KASAN UAF can produce a kernel fault or panic depending on runtime configuration. This is counted once only.

No negative signals were applied:

* No host-admin penalty. The supplied patch and description show a tracefs histogram-trigger write path, but do not positively establish that every vulnerable deployment requires host-admin-equivalent privilege. Typical tracefs permissions are not sufficient proof for HostAdminRequired=YES under the requested rules.
* No hard-race penalty. The vulnerable sequence is an ordered failed-enable and cleanup sequence, not a demonstrated narrow timing race.
* No niche-subsystem penalty. Tracing configuration is not automatically scored as rare or unreachable merely because it is a control-plane interface.

Material non-awarded signals:

* Controlled reclaim or replacement of the freed trigger object is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Remote reachability is not established. The trigger path is reached through local tracing configuration.
* Structured stale-object exploitation leverage is not awarded. The demonstrated stale use is a list traversal and stale-object read in find_named_trigger, not consumption of attacker-controlled replacement fields, callbacks, offsets, or operations.
* Weak LPE concern is not awarded solely because the defect is a UAF.
* Confidentiality and integrity points are not awarded. No disclosure path, unauthorized state modification, credential effect, or controlled post-free interpretation is demonstrated.
* Extra Availability is not awarded because the same stale dereference already supports the single crash or DoS point.
* Concrete repeated release or refcount mutation is not established. The supplied control flow shows a stale global list reference after freeing trigger_data, but does not show the exact same dangling trigger reference receiving a second put, free, or refcount decrement.
* The concrete repeated release/refcount +1 is therefore not awarded.
* Paranoid repeated-refcount leverage +1 is withheld.
* FLOOR 5 is not applied. This is a cleanup and unregister-related UAF with demonstrated stale traversal, but no concrete second lifetime mutation, controlled reuse, or post-free active structured processing beyond the stale lookup is shown.

## 3. Reachability analysis

The direct trigger is a local write to the tracing event-trigger interface which reaches event_trigger_write, event_hist_trigger_parse, hist_register_trigger, and the failed histogram-trigger enable path.

The supplied evidence does not prove the complete privilege boundary. In common host configurations, tracefs control files are owned by root and creating histogram triggers normally requires administrative access or explicitly delegated write permissions. However, the patch alone does not establish whether the relevant tracefs instance can be writable by a non-host-admin service, tracing daemon, container, or delegated operator.

HostAdminRequired is therefore UNKNOWN rather than YES. The input supports neither a proven ordinary-user trigger nor a proven requirement for host-root-equivalent privilege.

NamespaceScopedPrivilege is UNKNOWN. No evidence establishes that the complete tracefs histogram-trigger creation, failed enable operation, unregister path, and later named-trigger lookup can be performed entirely with attacker-obtainable namespaced capabilities. The mere possibility of containers or namespaces is insufficient.

No remote packet, socket, device, firmware, or network protocol input reaches this path directly. Prior host setup may be required in practice because tracing must be available and writable, but the supplied evidence does not prove a separate privileged provisioning prerequisite beyond access to the trace interface.

The failure is not presented as a narrow timing-dependent race. The relevant path is an ordered error-handling sequence: registration, failed enable, premature removal from file triggers, unregister failure to find the trigger, freeing of trigger_data, and later traversal of the stale global named_triggers entry.

## 4. Primitive and severity interpretation

The exact primitive is a real heap lifetime violation. A histogram trigger is registered in the global named_triggers list, then removed from the per-file trigger list when enablement fails. The later unregister logic searches only the per-file list, fails to find the trigger, skips the cleanup that removes the global named-triggers registration, and the error path frees trigger_data anyway. The global list retains a stale reference to freed storage.

This is an active structured object rather than fixed stale storage because the freed trigger remains reachable through a global lookup list. However, the demonstrated stale use is constrained: find_named_trigger performs a stale traversal/read. The supplied patch does not establish attacker-controlled replacement, controlled heap reuse, callback dispatch from reclaimed contents, arbitrary read/write, or a security-sensitive field being consumed after replacement.

This is not a concrete repeated release/refcount case. The first free can end the trigger lifetime. A stale global-list reference survives. But the supplied evidence does not establish that the exact same trigger reference receives a second free, put, kref operation, or other write-like lifetime mutation. The additional issue involving hist_data is also a post-free access ordering problem, not a demonstrated second lifetime mutation on the same object.

PrimitiveClass is CLASS_B because a confirmed UAF exists and the object remains globally reachable after free. The demonstrated practical consequence is kernel memory safety failure and likely local DoS. Privilege escalation, confidentiality impact, integrity impact, controlled corruption, and callback control remain speculative and are not scored.

ImportantCandidate is NO because this is currently a constrained cleanup and failed-registration UAF. Meaningful exploitation leverage beyond crash has not been established. AutoDowngradeAllowed is YES because there is no demonstrated repeated lifetime mutation, controlled reclaim, active replacement primitive, security-boundary bypass, or post-free write-like operation requiring Important-versus-Moderate preservation. Manual review remains recommended due to the confirmed kernel UAF and unresolved deployment privilege boundary.

Likely operational severity is Borderline Moderate. It should be patched in normal maintenance, and deployments that delegate write access to tracefs should verify actual reachability before automatically prioritizing it as Important.

## 5. One-sentence report phrase

A failed tracing histogram-trigger enable operation can leave a freed trigger referenced by the global named_triggers list, allowing a later lookup to dereference stale memory and cause a local kernel crash or denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The patch confirms a real UAF, but the supplied evidence does not establish controlled reclaim, repeated refcount corruption, privilege escalation, or the exact privilege boundary for the complete tracefs trigger path.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: tracing: Undo the registration when enabling the histogram trigger fails [ Upstream
Commit: 51b07104d563d4be2be34158d3b9d922ca417642
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51b07104d563d4be2be34158d3b9d922ca417642

Changed files:
  kernel/20260907092944.3950E1F00A3D
  kernel/trace/trace_events_hist.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=51b07104d563d4be2be34158d3b9d922ca417642

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

The original Linux kernel CVE announcement for CVE-2026-97918 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97918

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:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 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).