[CVE-2026-93275][LOW] perf/x86/intel/pt: Fix stop/start with no update [ Upstream

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

CVE: CVE-2026-93275
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: perf/x86/intel/pt: Fix stop/start with no update [ Upstream
Commit: 9b919fb5512f256e9e0604faf960b2bb98aab454
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9b919fb5512f256e9e0604faf960b2bb98aab454
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93275
Analysis date: Thu, 24 Sep 2026 19:01:41 -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-2026-93275 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93275

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-2026-93275	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93275 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:N/I:N/A:L';CWE-703;*CWE-664;CWE-670;BEST CVSS score: '2.5';DESCR 'An Intel PT perf event can reach an inconsistent AUX output state when group throttling calls stop and start without PERF_EF_UPDATE. A subsequent start can invoke perf_aux_output_begin while the previous AUX output context is still open and trigger a kernel WARNING. For the CVSS the PR:L is used because a local user must create and run a suitable perf event. Exploitation also requires Intel PT support, AUX sampling, a grouped event, and a throttling condition, so AC:H is appropriate. The issue is not network reachable. Impact is limited to tracing disruption and possible low availability impact. The provided code does not show a use-after-free, out-of-bounds access, NULL dereference, information leak, or write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	WARNONLY HARDWARE 	NO	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +0 Invalid state and WARN only. The established consequence is an unbalanced perf AUX output begin and end state which triggers WARN_ON in perf_aux_output_begin.
* +0 No reliable kernel crash or strong DoS is established. A warning and Intel PT tracing disruption are not independently demonstrated as host-wide availability failure.
* +0 No UAF, stale post-free access, refcount mutation, double release, OOB access, invalid dereference, arbitrary write, information disclosure, or authorization bypass is established.
* +0 Local unprivileged trigger is not awarded. The patch demonstrates use of perf events but does not establish that the complete Intel PT AUX sampling and group throttling sequence is available to an ordinary user in the evaluated deployment.
* +0 Remote reachability is not established.
* +0 Controlled reclaim, structured stale-object leverage, arbitrary write, confidentiality impact, integrity impact, and LPE are not demonstrated.
* +0 No race penalty is applied. This is a deterministic state-management issue involving throttling callbacks, not a demonstrated narrow timing race.
* +0 No host-admin penalty is applied because host-admin-equivalent privilege is not positively established.

3. Reachability analysis

The issue is triggered through a local perf Intel PT event using AUX sampling and a grouped event that becomes throttled. Intel PT hardware support is required. Access to perf_event_open and Intel PT tracing is controlled by system perf policy such as perf_event_paranoid and may be restricted in hardened deployments, but the supplied patch does not establish that host administrator privilege is required for the complete trigger sequence.

The example changes /proc/sys/kernel/perf_event_max_sample_rate, which normally requires administrative privilege. However, this is an example used to reproduce throttling and does not prove that changing this sysctl is required for every trigger. Therefore HostAdminRequired is UNKNOWN rather than YES.

The relevant perf and PMU access checks are not a namespace-scoped capability path. There is no evidence that an attacker-created namespace permits the complete Intel PT perf event setup and trigger sequence. NamespaceScopedPrivilege is NO.

4. Primitive and severity interpretation

The exact defect is a perf AUX output state-machine inconsistency. pt_event_stop without PERF_EF_UPDATE can leave an AUX output context open, and a later pt_event_start can call perf_aux_output_begin again despite the open context. This violates the non-nesting invariant and produces a kernel WARNING.

This is neither an active structured-object UAF nor fixed stale storage. There is no object free, stale dereference, repeated put, refcount decrement, post-free mutation, or memory ownership violation. The patch uses PERF_HES_UPTODATE to represent whether the existing AUX context has been closed and to balance perf_aux_output_begin with perf_aux_output_end.

PrimitiveClass is NONE. The demonstrated consequence is a warning and potentially disrupted Intel PT tracing. A kernel panic, memory corruption, information disclosure, integrity impact, privilege escalation, and network attack path are speculative and unsupported. ImportantCandidate is NO, and AutoDowngradeAllowed is YES because no unresolved corruption or security-boundary primitive remains.

5. One-sentence report phrase

An Intel PT perf event can trigger a kernel WARNING when group throttling restarts an AUX sampling event with an already open AUX output context, causing tracing state inconsistency but no demonstrated memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch fixes a WARN-only AUX tracing state-management error without an established corruption, lifetime, authorization, disclosure, or privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: perf/x86/intel/pt: Fix stop/start with no update [ Upstream
Commit: 9b919fb5512f256e9e0604faf960b2bb98aab454
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9b919fb5512f256e9e0604faf960b2bb98aab454

Changed files:
  arch/x86/events/intel/pt.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=9b919fb5512f256e9e0604faf960b2bb98aab454

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

The original Linux kernel CVE announcement for CVE-2026-93275 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93275

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 2.5

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).