[CVE-2026-97919][MODERATE REGULAR] tracing: Take the reference before publishing the named histogram trigger [ Upstream

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

CVE: CVE-2026-97919
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tracing: Take the reference before publishing the named histogram trigger [ Upstream
Commit: 2ffaade3611bd9501bc0b9d5d19fc75bfee7a16b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ffaade3611bd9501bc0b9d5d19fc75bfee7a16b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97919
Analysis date: Fri, 25 Sep 2026 13:22:01 -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.

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

The original Linux kernel CVE announcement for CVE-2026-97919 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97919

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-2026-97919	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97919 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;CWE-404;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A named histogram trigger can remain published in the global named_triggers list when event_hist_trigger_init() fails during alloc_hist_pad(). The later error path frees the trigger without removing the published list entry, and a subsequent lookup by name accesses the freed object in find_named_trigger(). KASAN confirms a slab use after free with an eight byte read. The directly demonstrated impact is a local kernel crash and denial of service. The stale list entry and possible reuse of the freed slab object also create a plausible memory corruption risk that may allow confidentiality or integrity impact and in the worst case privilege escalation, although no reliable write primitive is established by the available code. For the CVSS the PR:L is used for the paranoid score because a local user may reach the path when tracing access is delegated through tracefs permissions, capabilities, container administration, or a tracing service. Normal systems usually restrict this interface to root or CAP_SYS_ADMIN, which supports PR:H for the base score. AC:H applies because triggering depends on an allocation failure followed by object cleanup and another named trigger lookup. The issue is not directly network reachable. Impact is at least a local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to the confirmed use after free and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)  SKIP CVE-2026-97919 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	READ TRACE UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

======================================================================
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 under REAL UAF FLOOR 4.
* Applied paranoid floor: 3 -> 4 under REAL UAF FLOOR 4.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF. A trigger is published in `named_triggers`, subsequently freed after initialization failure, and later accessed through the surviving list entry.
* +1 Reliable kernel crash or strong DoS. KASAN directly reports a slab use-after-free read in `find_named_trigger()`. A non-KASAN kernel can fault or process invalid object state.
* +0 Attacker-influenced lifetime manipulation. A writer controls trigger creation and the later name lookup, but reliable control over the required `alloc_hist_pad()` failure, reclaim, or post-free contents is not established.
* +0 Structured stale-object leverage. The stale object is globally published and structured, but the demonstrated stale operation is an eight-byte read during lookup. No meaningful replacement-object field consumption is established.
* +0 Strong or weak LPE leverage. Controlled reclaim, callback influence, arbitrary read/write, refcount takeover, and credential effects are not demonstrated.
* +0 Extra Availability. The same UAF crash is not counted twice.
* +0 Confidentiality and Integrity. No disclosure path, directed write, or unauthorized modification is shown.
* +0 Race penalty. This is an ordered initialization-error-cleanup sequence, not a demonstrated narrow timing race.
* +0 Privilege penalty. Tracefs trigger writes are commonly restricted, but the supplied evidence does not prove that host-admin-equivalent privilege is mandatory in every reachable configuration.
* +0 Remote reachability. No network-triggered path is established.
* First lifetime-ending operation: yes. `event_hist_trigger_parse()` can free the published trigger.
* Exact reference survives: yes. The global `named_triggers` entry remains.
* Second lifetime/refcount mutation: no. The demonstrated later operation reads the stale object rather than releasing it again.
* Concrete repeated release/refcount +1: not awarded.
* Paranoid repeated-refcount leverage +1: withheld.
* FLOOR 5: not applied. No concrete second lifetime mutation, controlled reclaim, attacker-shaped replacement, or nontrivial post-reuse processing is established.

3. Reachability analysis

The vulnerable path is reached by configuring named histogram triggers through tracing control files and then performing another lookup by name after initialization fails. The supplied material does not establish whether the complete operation requires immutable host-admin privilege or can be reached through delegated tracefs permissions, so `HostAdminRequired=UNKNOWN`.

No evidence establishes that tracing configuration is available through an attacker-created user or network namespace. Therefore, `NamespaceScopedPrivilege=UNKNOWN`. No special hardware is required, but kernel tracing and histogram-trigger support must be present and accessible.

The necessary allocation failure is a material prerequisite. The subsequent stale lookup is deterministic once the failed object has been freed while remaining published, but reliable attacker control over the allocation failure and slab reuse is not demonstrated. This is not a timing race.

4. Primitive and severity interpretation

The exact primitive is a stale pointer to a freed `event_trigger_data` object retained in the global named-trigger registry. It is an active structured object rather than fixed asynchronous storage, but the demonstrated post-free operation is a shallow lookup-time read in `find_named_trigger()`.

This is CLASS_B because an actual kernel lifetime violation and post-lifetime dereference are directly established. It is not CLASS_A because controlled reclaim, attacker-controlled replacement contents, arbitrary kernel access, callback control, refcount takeover, or privilege escalation is not established.

This is category A, an ordinary stale-object dereference, rather than category B, a concrete second lifetime/refcount mutation. The demonstrated consequence is KASAN detection and plausible kernel crash or DoS. Stronger exploitation through favorable slab reuse remains theoretical and is not scored.

`ImportantCandidate=NO` because the current evidence does not establish meaningful exploitation leverage beyond the stale read and crash path. `AutoDowngradeAllowed=YES` because there is no unresolved repeated release, controlled reuse, security-boundary bypass, or directed corruption primitive. Manual review remains recommended because the UAF escapes into a global registry rather than remaining confined to immediate cleanup.

5. One-sentence report phrase

A failed named histogram trigger initialization can leave a freed trigger reachable from the global named trigger list, causing a later lookup to perform a slab use after free and potentially crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The UAF is concrete, but available evidence supports a stale lookup read and DoS rather than an Important-grade exploitation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: tracing: Take the reference before publishing the named histogram trigger [ Upstream
Commit: 2ffaade3611bd9501bc0b9d5d19fc75bfee7a16b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2ffaade3611bd9501bc0b9d5d19fc75bfee7a16b

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=2ffaade3611bd9501bc0b9d5d19fc75bfee7a16b

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

The original Linux kernel CVE announcement for CVE-2026-97919 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97919

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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).