[CVE-2026-97935][MODERATE 7.0] tracing: Set the trace clock before registering the histogram trigger [ Upstream

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

CVE: CVE-2026-97935
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tracing: Set the trace clock before registering the histogram trigger [ Upstream
Commit: cfad128171f8e2237a3c723d6478ef2cfb3b9127
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cfad128171f8e2237a3c723d6478ef2cfb3b9127
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97935
Analysis date: Fri, 25 Sep 2026 15:23:30 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97935 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97935

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 7.0
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-2026-97935	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97935 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.8';DESCR 'A use-after-free in the tracing histogram named trigger path occurs when a trigger using common_timestamp with an invalid clock is published before tracing_set_clock rejects the clock. Error cleanup frees the trigger without removing it from global named_triggers, and a later trigger lookup by name dereferences freed kernel memory. A local actor able to write tracefs event trigger files can issue the failing configuration and then trigger a lookup using the same name. For the CVSS the PR:L paranoid value assumes tracefs trigger access has been delegated to a non administrative local service or container account. On conventional hosts this access is normally restricted to root or highly privileged tracing administrators. The immediate impact is a kernel crash. Because this is a confirmed kernel slab use-after-free, controlled reuse of the freed object could plausibly provide confidentiality or integrity impact and requires manual review. The issue is not directly network reachable.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	READ INIT TRACE UAF LINUS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	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
* Conservative floor applied: 3 -> 4. FLOOR 4 applies because a real non-fixed-storage UAF is demonstrated and host-admin-equivalent privilege is not positively established by the supplied evidence.
* Paranoid floor applied: 3 -> 4. No additional paranoid point is justified because controlled reclaim, post-free object replacement, arbitrary write, disclosure, or privilege escalation is not established.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation. The named histogram trigger is published on the global named_triggers list, later freed on the clock-validation failure path, and subsequently dereferenced by find_named_trigger. KASAN explicitly reports slab-use-after-free.
* +1 Reliable kernel crash / strong DoS. The supplied reproducer produces a KASAN UAF report during a later trigger lookup. On non-KASAN kernels this stale dereference can realistically result in an Oops or kernel crash.

No negative privilege penalty applied:

* Host-admin-equivalent privilege is not positively established in the supplied source context. Tracefs trigger writes are normally restricted in conventional deployments, but mount permissions and the exact capability or ownership checks are not included in the patch. UNKNOWN does not justify a -2 penalty.

Important non-awarded signals:

* Controlled reclaim or attacker-controlled replacement of the freed trigger object is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Remote reachability is not established. The trigger is exercised through local tracefs writes.
* Local unprivileged trigger is not awarded. The evidence does not establish that an ordinary user can write the relevant tracefs trigger file.
* Structured stale-object exploitation leverage is not awarded. The stale trigger is a structured object in a global list, but the demonstrated stale use is lookup and dereference only. There is no evidence that a reclaimed replacement object is consumed as valid attacker-controlled trigger state.
* Weak LPE concern is not awarded solely from the UAF class.
* Confidentiality and integrity points are not awarded. No read-back, disclosure, write primitive, callback influence, or protected-object modification is shown.
* Extra Availability is not awarded because the same stale dereference already accounts for the crash or DoS effect.
* No repeated release or refcount mutation exists. The patch shows publication, failure, freeing, and later lookup. It does not establish a second put, kfree, refcount decrement, or equivalent lifetime mutation through the same dangling reference.
* FLOOR 5 does not apply. There is no concrete second lifetime mutation, controlled reclaim, attacker-controlled post-free state, or demonstrated active processing beyond the stale lookup.

3. Reachability analysis

The evaluated attacker is a local process that can write to the tracefs event trigger interface, specifically the trigger file under an event such as sched_switch. The trigger sequence is ordered and does not require a timing race:

1. Submit a named histogram trigger using common_timestamp and an invalid clock.
2. The trigger is published before clock validation fails.
3. Error cleanup frees the trigger without unlinking it from named_triggers.
4. Submit another trigger using the same name, causing find_named_trigger to traverse the dangling list entry.

The supplied patch does not show VFS permissions, tracefs mount options, LSM policy, user namespace checks, or capability checks for writing event trigger files. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

NamespaceScopedPrivilege is UNKNOWN. No evidence establishes that an attacker-created user namespace or mount namespace can mount tracefs, access the relevant tracing instance, and complete the trigger-write sequence without host-level authorization. The existence of namespaces alone would not prove this.

The vulnerable feature requires tracing histogram trigger support and an accessible tracefs tracing interface. These are configuration and deployment factors, but no niche-subsystem penalty is applied because the attacker-accessible configuration boundary is unresolved rather than proven rare or inaccessible. No special hardware, firmware, sysctl, boot option, or race window is required by the demonstrated sequence.

4. Primitive and severity interpretation

The exact primitive is a real slab use-after-free. A named histogram trigger is made reachable through the global named_triggers list before a later clock-validation operation can fail. The failure path frees the trigger but leaves the global list pointing at freed memory. A subsequent lookup dereferences that freed object.

This is an active structured object rather than fixed stale storage. However, the demonstrated post-free operation is a shallow lookup through a stale global-list entry. The patch and supplied trace do not establish controlled replacement, attacker-shaped reclaimed contents, callback dispatch, pointer redirection, arbitrary read or write, refcount takeover, or an authorization-boundary bypass.

This is not an ordinary stale cleanup dereference because the stale object is used by a later lookup operation. It is also not a concrete repeated-release or refcount bug. The first lifetime operation is the freeing of the trigger during error cleanup, but no second lifetime-mutating operation on the same dangling trigger reference is shown.

PrimitiveClass is CLASS_B because a concrete kernel lifetime violation and stale structured-object dereference are established. ImportantCandidate is NO because the currently demonstrated consequence is crash or DoS, and meaningful exploitation leverage beyond the stale read is not established. AutoDowngradeAllowed is YES because this is currently a constrained Class B UAF with no demonstrated controlled reuse, write primitive, disclosure primitive, boundary bypass, or repeated lifetime mutation.

The supplied prior paranoid CVSS vector may be suitable for ensuring human attention to the UAF, but its hypothetical C:H and I:H impacts do not independently establish ActionableScore bonuses. The practical patch-supported conclusion is local authorized tracing-interface access leading to kernel DoS, with manual review warranted to verify tracefs permissions and potential object-reuse behavior in the affected kernel configuration.

5. One-sentence report phrase

A local writer of tracefs histogram triggers can create a named trigger with an invalid clock, leaving a freed trigger on the global named_triggers list and causing a later same-name lookup to dereference freed kernel memory and potentially crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Verify whether untrusted local users, delegated tracing services, containers, or monitoring agents can write the affected tracefs trigger files, and inspect find_named_trigger plus trigger object allocation behavior for any realistic controlled-reuse path.

7. Call-site confidence

Call-site confidence: medium

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

Patch: tracing: Set the trace clock before registering the histogram trigger [ Upstream
Commit: cfad128171f8e2237a3c723d6478ef2cfb3b9127
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cfad128171f8e2237a3c723d6478ef2cfb3b9127

Changed files:
  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=cfad128171f8e2237a3c723d6478ef2cfb3b9127

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

The original Linux kernel CVE announcement for CVE-2026-97935 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97935

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).