[CVE-2026-98552][LOW] perf/core: Fix a refcount leak in attach_perf_ctx_data() [ Upstream

[CVE-2026-98552][LOW] perf/core: Fix a refcount leak in attach_perf_ctx_data() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98552
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: perf/core: Fix a refcount leak in attach_perf_ctx_data() [ Upstream
Commit: 23250517cd475367653f1e99396967f54c6f1b7c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23250517cd475367653f1e99396967f54c6f1b7c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98552
Analysis date: Sat, 24 Oct 2026 09:24:49 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A race can leave perf context data permanently referenced by failing to mark the winning object global, causing a bounded-per-occurrence resource leak without shown memory corruption or host-wide DoS.

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

The original Linux kernel CVE announcement for CVE-2026-98552 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98552

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-2026-98552	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98552 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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:H';CWE-362;*CWE-772;*CWE-401;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race between global and non global perf context data attachment can leave an existing object with an increased reference count but lacking the global marker. Later global detach processing skips the matching task detach operation and the reference is retained. The demonstrated primitive is a persistent reference and resource leak rather than UAF or memory corruption. For the CVSS the PR:L value reflects that a local user or process must reach perf event operations and reliably exercise the racing attachment paths. AC:H reflects the required concurrency window. Base impact is limited resource retention with no demonstrated confidentiality or integrity effect and no established immediate host wide exhaustion. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	RACE LEAK HARDWARE LINUS 	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap applies.

2. Signal breakdown

* +1 Concrete persistent kernel reference/resource leak: the failed `try_cmpxchg()` path increments `old->refcount`, but without setting `old->global`; later global detach therefore skips the matching task detach and retains the reference.
* +0 Race penalty: concurrency is required, but the supplied evidence does not establish a narrow, one-shot, or externally uncontrollable race sufficient for −1.
* +0 Strong DoS: neither host-wide exhaustion nor a kernel crash is established.
* +0 UAF/corruption: the object is retained rather than prematurely freed; no OOB access, stale dereference, or overwrite is shown.
* +0 C/I or authorization impact: no disclosure, protected-state modification, or DENY-to-ALLOW decision exists.
* B5-R and B3-PENDING do not apply: there is no OOB/shared-backing write or later corrupted-state consumption.

3. Reachability analysis

Perf operations are locally reachable in some configurations, but the supplied patch does not establish the complete privilege requirements for both global and non-global attachment paths. Perf sysctls and capability checks may affect access, so host-admin and namespace-scoped reachability remain unknown. The attacker must induce concurrent attachment, but no special hardware or prior setup is shown.

4. Primitive and severity reading

The exact primitive is a persistent reference leak caused by inconsistent `global` metadata after a competing installation. It is a constrained CLASS_B lifetime/resource-management defect, not a UAF. The shown effect is retained perf context data; cumulative host-wide exhaustion is only theoretical. There is no authorization bypass, active-state corruption, or meaningful unknown Important-class leverage. Auto-downgrade is therefore allowed.

5. One-sentence report phrase

A race can leave perf context data permanently referenced by failing to mark the winning object global, causing a bounded-per-occurrence resource leak without shown memory corruption or host-wide DoS.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch establishes only a reference leak with no Important-preserving primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: perf/core: Fix a refcount leak in attach_perf_ctx_data() [ Upstream
Commit: 23250517cd475367653f1e99396967f54c6f1b7c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23250517cd475367653f1e99396967f54c6f1b7c

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=23250517cd475367653f1e99396967f54c6f1b7c

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

The original Linux kernel CVE announcement for CVE-2026-98552 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98552

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:L
  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: 1

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).