[CVE-2026-98268][LOW] perf: Fix null pointer access in is_include_guest_event() [ Upstream

[CVE-2026-98268][LOW] perf: Fix null pointer access in is_include_guest_event() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98268
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: perf: Fix null pointer access in is_include_guest_event() [ Upstream
Commit: 7fa9a465ae8f07c0e4685db6edb6a6f984dbd784
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7fa9a465ae8f07c0e4685db6edb6a6f984dbd784
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98268
Analysis date: Sat, 10 Oct 2026 16:18:55 -0400
ActionableScore: 0
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-2026-98268 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98268

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: LOW
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-2026-98268	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98268 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_LOW_ELIGIBLE_NO_POSITIVE_SIGNAL (independent Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-672;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference in the perf event release path can occur after PMU removal clears event pmu while an associated perf event remains open. Closing that event later can reach mediated_pmu_unaccount_event and is_include_guest_event, which previously accessed PMU capabilities through the NULL pointer and could cause a kernel Oops or panic. For the CVSS the PR:L value is used in the paranoid score because a local user may hold and close an allowed perf event while PMU removal is performed independently by the system or an administrator. This external lifecycle condition makes AC:H appropriate for that scenario. The issue is not network reachable. Impact is local denial of service only, with no supported UAF, information disclosure, or write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	DANGER NULLPTR UAF KERNEL_PANIC_PLUS_UAF HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: -1
* Paranoid score: 0
* Applied score lower bound: -1 -> 0
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash / strong DoS. Closing the remaining perf event after PMU detachment reaches a confirmed NULL dereference in `_free_event()`.
* -2 Full host-admin-equivalent prerequisite. The evidenced complete sequence includes PMU module unloading, which requires host `CAP_SYS_MODULE` or equivalent administrative control.
* +0 Weak corruption concern. The stale state is converted to an explicit NULL pointer and produces an invalid dereference rather than useful memory corruption.
* No UAF signal. `event->pmu` is explicitly cleared to prevent use of a freed PMU.
* No controlled reclaim, arbitrary write, repeated release, refcount mutation, disclosure, or authorization bypass is demonstrated.
* No extra Availability point. It would duplicate the already counted Oops or panic.
* No race penalty. The vulnerable sequence is ordered PMU detachment followed by event closure, not a demonstrated narrow timing race.
* No rarity penalty. Mediated vPMU use is specialized, but the evidence does not establish both rarity and exceptional reachability difficulty.
* B5-R is not applicable because no heap OOB write exists.
* B3-PENDING is not applicable because no shared-backing write exists.
* B4-PENDING is not applicable because no DENY-to-ALLOW authorization decision changes.

3. Reachability analysis

The demonstrated sequence requires an active perf event, PMU unregistration during module unloading, and later closure of the event. A local user may be able to own or close an allowed perf event, but the supplied evidence does not show that such a user can initiate the required PMU removal.

The complete evidenced trigger therefore depends on host-admin-equivalent module-management authority. Numeric host UID 0 is not strictly required because host `CAP_SYS_MODULE` is the relevant authority. This capability is not obtainable through an attacker-created user namespace for host module unloading, so the complete sequence is not namespace scoped.

An already loaded mediated-vPMU-capable PMU module and an active event are prerequisites. No direct network path, special race, or independently attacker-controlled object-reuse mechanism is established.

4. Primitive and severity interpretation

The exact primitive is a NULL pointer dereference. After `__pmu_detach_event()` clears `event->pmu`, later event cleanup calls `mediated_pmu_unaccount_event()` and previously dereferenced `event->pmu->capabilities`.

This is invalid-state consumption in a release path, not post-lifetime use of a non-NULL stale PMU object. The explicit comment `force fault instead of UAF` supports `RealUAF=NO`. There is no second release or refcount mutation through the cleared reference.

The demonstrated consequence is a kernel Oops or possible panic. Privilege escalation, information disclosure, controlled corruption, and useful behavior beyond the crash are unsupported. The issue is therefore CLASS_C, is not an Important candidate, and may be automatically downgraded after recording the affected configuration.

5. One-sentence report phrase

A host administrator unloading a mediated vPMU module while a perf event remains open can leave the event with a NULL PMU pointer that is dereferenced during later event release, causing a kernel Oops or panic.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a host-admin-dependent NULL dereference with crash-only impact and no UAF, write, disclosure, authorization bypass, or unresolved exploitation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: perf: Fix null pointer access in is_include_guest_event() [ Upstream
Commit: 7fa9a465ae8f07c0e4685db6edb6a6f984dbd784
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7fa9a465ae8f07c0e4685db6edb6a6f984dbd784

Changed files:
  kernel/events/core.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=7fa9a465ae8f07c0e4685db6edb6a6f984dbd784

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

The original Linux kernel CVE announcement for CVE-2026-98268 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98268

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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).