[CVE-2026-97960][MODERATE REGULAR] perf/x86/intel: Prevent drain_pebs() reentry [ Upstream

[CVE-2026-97960][MODERATE REGULAR] perf/x86/intel: Prevent drain_pebs() reentry [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97960
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: perf/x86/intel: Prevent drain_pebs() reentry [ Upstream
Commit: a5fe19dd8b3ed5fad6e5e0f0c58c7245043ee4af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a5fe19dd8b3ed5fad6e5e0f0c58c7245043ee4af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97960
Analysis date: Fri, 25 Sep 2026 14:37:41 -0400
ActionableScore: 2
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-2026-97960 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97960

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-97960	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97960 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-362;CWE-125;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A race condition in the Intel PEBS buffer draining path can allow drain_pebs to be reentered when a process context drain is interrupted by a performance monitoring interrupt from another active counter. Because the PEBS buffer is shared by events on the same CPU, the nested invocation can observe stale buffer state and potentially perform an out-of-bounds memory access. For the CVSS the PR:L rating is used because an attacker needs local access to the perf interface and the ability to create or control suitable performance events. The issue is not network reachable. The confirmed impact is at least local denial of service through a kernel warning or crash. The potential out-of-bounds access warrants manual review for limited confidentiality impact, but the patch does not demonstrate a write primitive, UAF, or a practical privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	WRITE OOB HARDWARE  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied. The available patch evidence establishes a reentry race and a potential out of bounds access, but does not establish a write, disclosure, UAF, controlled replacement, or privilege escalation primitive.

2. Signal breakdown

* +1 Weak invalid memory access concern. The commit explicitly states that reentered drain_pebs may observe stale PEBS buffer state and potentially access out of bounds memory. This supports CWE-362 and a potential CWE-125 style invalid read condition. CWE-787 is not established because no write is shown.
* +1 Potential kernel DoS. Invalid PEBS buffer state during kernel PMU processing can plausibly result in a kernel warning, fault, or crash. This is counted once only.

Important non-awarded signals:

* +0 Real UAF. No object is freed and later accessed. The stale state is PEBS buffer bookkeeping, not a post-free object reference.
* +0 Controlled reclaim or object replacement. Not demonstrated.
* +0 Arbitrary or directed kernel write. Not demonstrated.
* +0 Confidentiality impact. No kernel memory contents are shown to be copied to userspace, network output, or another observable interface.
* +0 Integrity impact. The patch does not establish an out of bounds write or corruption of an active security relevant object.
* +0 Local unprivileged trigger. The affected path uses perf and PEBS functionality, but the supplied material does not establish that an ordinary unprivileged user can create all required PEBS events under the evaluated perf_event_paranoid policy.
* +0 Remote reachability. Not network reachable.
* +0 Hard race penalty. Reentry requires a PMI while a process-context drain is in progress, but the evidence does not establish that the timing is rare, one-shot, or impractical to repeat.
* +0 niche or hardware penalty. PEBS requires compatible Intel PMU hardware, but Intel PEBS-capable systems are not sufficiently rare to justify a penalty based only on the supplied evidence.

3. Reachability analysis

The relevant attacker model is a local process that can create, enable, stop, or otherwise control suitable Intel PEBS perf events. The vulnerable sequence requires a process-context PEBS drain while another active PMU counter can generate a PMI and interrupt the drain operation.

The supplied patch does not establish the exact perf_event_open permissions, perf_event_paranoid configuration, or whether raw PEBS event setup is available to an ordinary user on the evaluated system. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

No namespace-specific capability path is shown. Creating a user or network namespace does not by itself prove that the complete Intel PMU and PEBS event setup is available there. NamespaceScopedPrivilege is UNKNOWN.

No remote packet, device firmware input, guest-to-host path, or prior host-created topology is shown. Relevant prerequisites are Intel hardware supporting PEBS and a kernel configuration and perf policy that permit the required events. The process-context drain and interrupt reentry condition is repeatable in principle, but practical reliability requires hardware and event-state validation.

4. Primitive and severity interpretation

The exact primitive is a PMU reentry race. A process-context invocation of intel_pmu_drain_pebs_buffer may run while the PMU is not fully disabled. A PMI from another active counter can then invoke PEBS draining again on the same CPU. The nested drain may use stale shared PEBS buffer state and potentially access memory outside the intended PEBS buffer bounds.

This is not a UAF, double release, refcount mutation, active-object replacement, or ownership violation. It is also not a demonstrated out of bounds write. The visible patch prevents the condition by quiescing the full PMU around the relevant drain and adds a warning when draining occurs while the PMU remains enabled.

The demonstrated consequence is invalid PMU buffer processing with a plausible local kernel crash or DoS. A confidentiality consequence is speculative because no read-back path is established. Integrity impact and privilege escalation are speculative because no write primitive, controlled object reuse, callback influence, or attacker-controlled post-corruption state is shown.

PrimitiveClass is CLASS_C because the established behavior is primarily race-driven invalid-state handling and potential crash behavior without an independently useful memory-corruption primitive. ImportantCandidate is NO because the current evidence does not leave a strong Important-versus-Moderate exploitation primitive unresolved. AutoDowngradeAllowed is YES because the issue may be treated as ordinary Moderate after confirming that the PEBS drain implementation does not turn stale buffer indices into a write or externally observable disclosure.

Likely operational severity is local Moderate DoS on affected Intel PEBS-enabled systems with suitable perf access.

5. One-sentence report phrase

A race in Intel PEBS buffer draining can allow a PMI to reenter drain_pebs while a process-context drain is active, potentially causing stale buffer state and an out of bounds kernel memory access that may result in local denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review the architecture-specific x86_pmu_drain_pebs implementation and PEBS buffer index handling to determine whether the stale state can cause only an invalid read and crash, or whether it can reach a write, data disclosure, or attacker-influenced buffer pointer or length.

7. Call-site confidence

Call-site confidence: medium

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

Patch: perf/x86/intel: Prevent drain_pebs() reentry [ Upstream
Commit: a5fe19dd8b3ed5fad6e5e0f0c58c7245043ee4af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a5fe19dd8b3ed5fad6e5e0f0c58c7245043ee4af

Changed files:
  arch/x86/events/intel/core.c
  arch/x86/events/intel/ds.c
  arch/x86/events/perf_event.h

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=a5fe19dd8b3ed5fad6e5e0f0c58c7245043ee4af

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

The original Linux kernel CVE announcement for CVE-2026-97960 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97960

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:L/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:L/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 2

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).