* [CVE-2026-98972][MODERATE REGULAR] cgroup/cpuset: Don't access cpuset_cgrp_subsys.root in is_in_v2_mode() [ Upstream
@ 2026-10-27 7:24 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-27 7:24 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98972
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cgroup/cpuset: Don't access cpuset_cgrp_subsys.root in is_in_v2_mode() [ Upstream
Commit: 988bf67a13890a37a33201f95947095ca9bec856
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=988bf67a13890a37a33201f95947095ca9bec856
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98972
Analysis date: Tue, 27 Oct 2026 03:24:27 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A concurrent cgroup rebind can leave `is_in_v2_mode()` reading a freed cgroup-root flags field, potentially crashing the kernel or selecting incorrect cpuset behavior.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98972 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98972
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98972 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98972 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A stale cpuset_cgrp_subsys root pointer can be dereferenced by is_in_v2_mode while a cgroup filesystem is being rebound, creating a use after free read of the root flags field. The directly supported impact is a local kernel crash, while reuse of the freed object could also select an incorrect cpuset mode and affect CPU mask handling. No arbitrary write or direct information disclosure primitive is established, but the kernel UAF and object reuse implications justify a paranoid memory corruption assessment. For the CVSS the PR:L paranoid value represents environments where reduced capability administrators or management services can initiate cgroup rebind operations, while reliable direct triggering normally requires stronger cgroup administration privileges. The race and privileged control path are not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE DANGER SIMPLEFIX HARDWARE LINUS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 4. REAL UAF FLOOR 4 applies because a stale structured root is actually read, this is not fixed stale storage, and host-admin-equivalent privilege is not positively established.
* Raw paranoid score: 3.
* Paranoid score: 4. No additional technically supported leverage signal exists.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 — Real UAF/lifetime violation: `is_in_v2_mode()` can dereference the stale `cpuset_cgrp_subsys.root` and read its `flags`.
* +1 — Plausible kernel crash: dereferencing a freed root during concurrent cgroup rebinding can fault.
* +0 — Wrong cpuset mode may influence subsequent CPU-mask handling, but attacker-shaped reuse, controlled replacement, or a directed write is not shown.
* Floor 4 — Active structured storage is read outside its lifetime; host-admin-only reachability is unresolved.
* No race penalty: the patch establishes concurrency but not a demonstrably narrow or unreliable race.
* No structured stale-object leverage, arbitrary write, controlled reclaim, disclosure, integrity impact, repeated refcount mutation, or authorization bypass is shown.
* No extra availability point: it would duplicate the same possible crash.
3. Reachability analysis
The vulnerable window involves cgroup filesystem rebinding concurrent with an `is_in_v2_mode()` caller. Rebinding ordinarily involves cgroup administration, but the supplied evidence does not establish whether the complete trigger requires effective host-administrator power or can be exercised through delegated/user-namespace administration. Thus both host-admin and namespace-scoped privilege remain unknown. No remote path, special hardware, prior attacker-accessible setup, or proven repeatable race strategy is shown.
4. Primitive and severity reading
The primitive is a read use-after-free of an active `cgroup_root` field. The stale `flags` value is consumed to choose cpuset mode, so this is more than passive diagnostic access, but the patch only establishes an invalid read and possible crash or incorrect mode selection. It does not show post-free writes, attacker-controlled reclaimed contents, callbacks, sensitive ownership changes, or a concrete cross-boundary consumer. This is CLASS_B, but presently constrained enough that ImportantCandidate is NO and automatic Moderate handling remains permissible after review.
5. One-sentence report phrase
A concurrent cgroup rebind can leave `is_in_v2_mode()` reading a freed cgroup-root flags field, potentially crashing the kernel or selecting incorrect cpuset behavior.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm the complete privilege boundary, race reachability, and whether wrong-mode CPU-mask processing has effects beyond a crash.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: cgroup/cpuset: Don't access cpuset_cgrp_subsys.root in is_in_v2_mode() [ Upstream
Commit: 988bf67a13890a37a33201f95947095ca9bec856
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=988bf67a13890a37a33201f95947095ca9bec856
Changed files:
kernel/cgroup/cpuset.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=988bf67a13890a37a33201f95947095ca9bec856
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98972 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98972
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:H/I:H/A:H
The Best / paranoid CVSS score: 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: 4
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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