[CVE-2026-98506][MODERATE 7.0] mm/hugetlb: do not dissolve gigantic pages without runtime support [ Upstream

[CVE-2026-98506][MODERATE 7.0] mm/hugetlb: do not dissolve gigantic pages without runtime support [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98506
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mm/hugetlb: do not dissolve gigantic pages without runtime support [ Upstream
Commit: ddc1055b557506a6ea8930dfbd8d1555d6a3f01e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddc1055b557506a6ea8930dfbd8d1555d6a3f01e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98506
Analysis date: Sat, 24 Oct 2026 12:47:44 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
Gigantic-page dissolution can free a still-listed folio or re-add it during rollback, leaving active hugetlb free-list lifetime and structural corruption for later kernel consumers.

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

The original Linux kernel CVE announcement for CVE-2026-98506 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98506

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 7.0
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-2026-98506	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98506 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both 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-415;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'dissolve_free_hugetlb_folio can process a gigantic hugetlb folio even when its hstate does not support runtime allocation or freeing. The lower level removal paths then bail out and the physical folio can be freed while it remains linked on the hugetlb free list. A vmemmap restoration failure can also invoke add_hugetlb_folio for an object that is still listed and corrupt the list directly. This is a local memory lifetime and list corruption issue with plausible use after free consequences rather than a crash only defect. For the CVSS the PR:L value in the paranoid vector reflects environments where a restricted service account or delegated capability can reach a memory management path that dissolves huge pages. The issue is not directly network reachable and reliable triggering requires gigantic pages without runtime support plus a suitable page dissolution operation. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because a specific evidence based protection or manual review veto was applied and FD false positive review allowed a downgrade. 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 4.2 and ActionableScore 3 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	READ INIT SIMPLEFIX LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
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 freed storage remains represented by an active hugetlb free-list entry and host-admin-only reachability is not established.
* Raw paranoid score: 5.
* Paranoid score: 5. No additional floor or cap.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 — Real lifetime violation: lower removal helpers silently bail, but the folio can still be physically freed while linked on the hugetlb free list.
* +1 — Separate direct list corruption: if vmemmap restoration fails, rollback calls `add_hugetlb_folio()` for an already-listed folio.
* +1 — Reliable kernel crash/strong DoS is plausible from later traversal of stale or structurally corrupted free-list state.
* -1 — The path requires gigantic hugetlb pages without runtime allocation/free support, a boot/configuration-dependent state attackers cannot ordinarily instantiate.
* Paranoid +1 — Normal free-list semantics support later consumption for folio selection and list traversal; this is material active structured-state use beyond merely recording stale metadata.
* Not awarded: controlled reclaim, attacker-selected payload/target, arbitrary write, disclosure, integrity impact, LPE, or remote reachability.
* NEW52/B5-R does not apply: no retry-accumulated OOB write is shown.
* No extra Availability point; it would duplicate the same potential kernel failure.

3. Reachability analysis

The supplied patch establishes the corruption mechanics but does not expose callers or the privilege checks governing the complete dissolution operation. The hints describe possible delegated-service reachability, but do not prove a below-host-admin trigger or namespace-scoped capability chain. Gigantic pages without runtime support require prior host configuration. No special hardware or timing race is shown; vmemmap restoration failure is an additional state-dependent condition.

4. Primitive and severity reading

This is active structured-state lifetime corruption, not fixed stale storage: a folio may be freed without retirement from the hugetlb free list, and rollback can directly corrupt that list by adding it again. Later privileged hugetlb list operations can consume the stale folio identity and list links.

The evidence supports CLASS_B rather than CLASS_A because controlled reclaim, directed corruption, and an attacker-shaped adjacent victim are not shown. ImportantCandidate is YES because concrete active free-list corruption and a privileged later consumer are established while the delegated/local trust boundary and resulting exploit leverage remain unresolved. Auto-downgrade is unsafe despite the absence of proven LPE.

5. One-sentence report phrase

Gigantic-page dissolution can free a still-listed folio or re-add it during rollback, leaving active hugetlb free-list lifetime and structural corruption for later kernel consumers.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm dissolution call sites, effective privilege requirements, delegated-service exposure, and whether later allocation can consume attacker-influenced reclaimed folio state.

7. Call-site confidence

Call-site confidence: medium

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

Patch: mm/hugetlb: do not dissolve gigantic pages without runtime support [ Upstream
Commit: ddc1055b557506a6ea8930dfbd8d1555d6a3f01e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddc1055b557506a6ea8930dfbd8d1555d6a3f01e

Changed files:
  mm/hugetlb.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=ddc1055b557506a6ea8930dfbd8d1555d6a3f01e

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

The original Linux kernel CVE announcement for CVE-2026-98506 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98506

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:L/I:L/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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).