* [CVE-2026-93181][LOW] perf/x86/intel/uncore: Fix uncore_box ref/unref ordering [ Upstream
@ 2026-09-18 5:00 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 5:00 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93181
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: perf/x86/intel/uncore: Fix uncore_box ref/unref ordering [ Upstream
Commit: 64aa1bb4017d598828c6d8cd718f43daf2a83375
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=64aa1bb4017d598828c6d8cd718f43daf2a83375
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93181
Analysis date: Fri, 18 Sep 2026 01:00:30 -0400
ActionableScore: 1
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-2026-93181 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93181
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-2026-93181 LOW https://www.kernelcve.org/list/?q=CVE-2026-93181 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:L/I:L/A:H';CWE-911;*CWE-664;*CWE-416;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'Intel uncore PMU CPU hotplug handling can use the wrong refcount and context ordering for uncore boxes. A box may fail to initialize on the first CPU of a die, or its refcount may be one count below the real number of users and allow teardown before the last CPU in the die is offline. For the CVSS the PR:L is used in the paranoid score because delegated CPU hotplug or perf management may be available to a reduced capability local administrator or service account, while normal host configurations are closer to PR:H. The issue is not network reachable and is triggered through local CPU hotplug or uncore PMU management paths. Impact is at least local denial of service or loss of uncore PMU functionality, and in the worst case may involve limited confidentiality or integrity impact if premature teardown leads to a use after free style lifetime bug.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES NOMEMCHK HARDWARE YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
No floor was applied. Real UAF floor 4 is not applied because host-admin-equivalent CPU hotplug control is positively established as the practical trigger path.
2. Signal breakdown
Positive signals:
* +2 Real UAF / active lifetime violation. The refcount can be one count below the real number of users, allowing an uncore box to be torn down before the true last CPU in the die is offline.
* +1 Limited availability / functional DoS. The bug can leave the uncore PMU box permanently uninitialized or torn down too early, causing loss or breakage of uncore PMU functionality.
Negative signals:
* -2 Host-admin-equivalent trigger requirement. The relevant path is CPU online/offline hotplug handling, which is normally controlled through host administrative CPU hotplug mechanisms.
Non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Remote reachability not established.
* Local ordinary user trigger not established.
* Namespace-scoped privilege not established.
* Strong LPE leverage not awarded.
* Structured stale-object exploitation leverage not awarded because attacker-controlled replacement or attacker-shaped post-free contents are not shown.
* Concrete repeated release/refcount signal not awarded. The patch establishes refcount undercount and premature teardown, but does not visibly establish that the exact same dangling reference deterministically receives a second lifetime-mutating put/free after the first teardown.
* Extra availability not awarded because there is no distinct host-wide crash or persistent system-wide failure shown.
* C/I impact not awarded merely because premature teardown could theoretically become memory corruption.
Repeated-release/refcount check:
* First release can end lifetime: possibly yes, because undercount can make teardown occur early.
* Exact same reference survives: not established from the supplied diff.
* Second operation is a real lifetime/refcount mutation: not concretely established from visible control flow.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.
3. Reachability analysis
The vulnerable code is in Intel uncore PMU CPU hotplug callbacks. The practical trigger requires changing CPU online/offline state or otherwise exercising CPU hotplug transitions. That is host-admin-equivalent on normal Linux systems.
Ordinary unprivileged reachability is not established. A local user may be able to use perf in some configurations, but the supplied evidence does not show that perf_event_open alone can drive the faulty online/offline lifetime sequence. Namespace-scoped capability is not applicable because CPU hotplug over host CPUs is not a network or user namespace scoped operation.
No remote or packet-based trigger exists. No prior special attacker-controlled setup is shown beyond requiring affected Intel uncore PMU hardware and CPU hotplug activity. The hardware is Intel-specific but not treated as rare hardware for scoring. There is no timing race penalty because the issue is mainly wrong ordering and refcount accounting, not a narrow attacker-won race.
4. Primitive and severity interpretation
The primitive is a refcount and lifetime-ordering bug in uncore box management. The object is an active structured kernel object, not fixed stale storage. The patch indicates that the box may be left uninitialized or may be torn down before all logical users are gone.
This supports PrimitiveClass=CLASS_B because a real active-object lifetime violation is directly implied. RealUAF=YES is used because final lifetime teardown may occur while a true user still exists. However, the demonstrated consequence is primarily broken uncore PMU state or local availability impact. There is no demonstrated controlled reclaim, attacker-shaped replacement, arbitrary read/write, callback control, credential impact, or security-boundary bypass.
ImportantCandidate=NO because the complete reachable attacker model appears host-admin controlled and the unresolved exploitation leverage is weak. AutoDowngradeAllowed=YES because this is a constrained host-admin-triggered lifetime bug with no concrete repeated lifetime mutation, no below-host-admin reachability, and no demonstrated security-boundary consequence.
Operational severity is ordinary Moderate or Low-like for security triage, despite being a real kernel lifetime bug.
5. One-sentence report phrase
Intel uncore PMU CPU hotplug handling used incorrect ref and unref ordering, which could leave uncore boxes uninitialized or torn down before the true last CPU user is gone, but practical triggering appears to require host-admin CPU hotplug control and no concrete privilege escalation primitive is shown.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: this is a real lifetime/refcount ordering issue in an active kernel object, but the visible evidence points to host-admin-triggered PMU breakage rather than a below-host-admin security primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: perf/x86/intel/uncore: Fix uncore_box ref/unref ordering [ Upstream
Commit: 64aa1bb4017d598828c6d8cd718f43daf2a83375
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=64aa1bb4017d598828c6d8cd718f43daf2a83375
Changed files:
arch/x86/events/intel/uncore.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=64aa1bb4017d598828c6d8cd718f43daf2a83375
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93181 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93181
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:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.8
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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