* [CVE-2026-93172][LOW] mm/mm_init: handle alloc_percpu failure in free_area_init_core_hotplug [ Upstream
@ 2026-09-18 7:44 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 7:44 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93172
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/mm_init: handle alloc_percpu failure in free_area_init_core_hotplug [ Upstream
Commit: 4cc5caef9a8d1894dfa31d84a0daa0ac1437dadc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cc5caef9a8d1894dfa31d84a0daa0ac1437dadc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93172
Analysis date: Fri, 18 Sep 2026 03:44:29 -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-2026-93172 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93172
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-2026-93172 LOW https://www.kernelcve.org/list/?q=CVE-2026-93172 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-252;**CWE-476;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference can occur in the memory hotplug path because free_area_init_core_hotplug did not check alloc_percpu failure for pgdat per_cpu_nodestats. If the allocation fails, later code may offset into a NULL per CPU pointer during node online initialization and crash the kernel. For the CVSS the PR:H is typical because reliable triggering requires administrative control over memory hotplug or equivalent host management privileges. The issue is not network reachable and depends on a local memory hotplug operation plus an allocation failure condition. Impact is denial of service via kernel crash or failed node online operation. No direct confidentiality or integrity impact is indicated because the primitive is a NULL pointer dereference rather than UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE INIT NOMEMCHK SIMPLEFIX HARDWARE DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: -1
* Conservative score: 0
* Raw paranoid score: -1
* Paranoid score: 0
* Applied conservative floor/cap: raw -1 was clamped to 0
* Applied paranoid floor/cap: raw -1 was clamped to 0
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +1 Reliable kernel crash / strong DoS: unchecked alloc_percpu failure can leave pgdat->per_cpu_nodestats unusable for later per-cpu offset access, resulting in a NULL pointer dereference during memory hotplug node initialization.
Negative signals:
* -2 Host-admin-equivalent privilege required: the affected path is memory hotplug node online initialization, which is a host management operation normally requiring host root or equivalent host administrative control.
Non-awarded material signals:
* Real UAF not awarded: the patch fixes an unchecked allocation failure and NULL dereference, not stale post-lifetime object use.
* Concrete repeated release/refcount not awarded: no first release, surviving dangling reference, or second lifetime mutation is present.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity not awarded: the established primitive is NULL pointer dereference / failed initialization, not disclosure, OOB access, UAF, or write corruption.
* Remote reachability not established.
* Local unprivileged trigger not awarded: no evidence shows an ordinary user can perform the complete memory hotplug operation.
* Extra Availability not awarded: the only availability effect is the same crash or failed hotplug operation already counted.
* No rare-subsystem penalty was applied: memory hotplug may be configuration-dependent, but the concrete reducing factor is the host-admin management requirement.
3. Reachability analysis
The vulnerable operation is reached through memory hotplug initialization for a node, specifically hotadd_init_pgdat() calling free_area_init_core_hotplug(). The complete trigger requires initiating or controlling memory hotplug / node online behavior and also reaching an alloc_percpu failure condition.
This is not a namespace-scoped operation. The relevant control is host-level memory management, not an attacker-created user or network namespace capability. There is no network path. There is no evidence that an ordinary local user can instantiate the vulnerable operation. There is no race dependency. The allocation failure condition may require memory pressure or fault-injection-like conditions, but no separate timing penalty is needed because the primary limiting factor is host-admin reachability.
4. Primitive and severity interpretation
The exact primitive is an unchecked allocation failure leading to NULL pointer dereference when per_cpu_nodestats is later used as a per-cpu pointer. This is CLASS_C invalid-state / crash behavior.
It is not active structured UAF and not fixed stale storage UAF. It is not cleanup/destructor post-lifetime use. It has no concrete repeated release/refcount operation. The demonstrated consequence is kernel crash or failed memory hotplug node online operation. The speculative consequence beyond DoS is weak because the bug does not provide controlled memory corruption, object reuse, arbitrary read/write, or authorization bypass.
ImportantCandidate=NO because no Class A primitive and no meaningful Class B unresolved exploitation leverage is established. AutoDowngradeAllowed=YES because this is a host-admin-gated NULL dereference / DoS-only issue with no unresolved memory-corruption or security-boundary primitive.
Likely operational severity: ordinary Moderate / Low-like, mainly relevant for robustness of memory hotplug error handling rather than urgent security response.
5. One-sentence report phrase
A NULL pointer dereference in the memory hotplug path can occur when free_area_init_core_hotplug() fails to check alloc_percpu() for pgdat per_cpu_nodestats, allowing a host-admin-triggered node online attempt under allocation failure to crash the kernel or fail the hotplug operation.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The issue is host-admin-gated, not network reachable, and the established primitive is NULL dereference / DoS only with no UAF, repeated refcount mutation, authorization bypass, disclosure, or write-corruption primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mm/mm_init: handle alloc_percpu failure in free_area_init_core_hotplug [ Upstream
Commit: 4cc5caef9a8d1894dfa31d84a0daa0ac1437dadc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cc5caef9a8d1894dfa31d84a0daa0ac1437dadc
Changed files:
include/linux/memory_hotplug.h
mm/memory_hotplug.c
mm/mm_init.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=4cc5caef9a8d1894dfa31d84a0daa0ac1437dadc
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93172 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93172
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: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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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