* [CVE-2026-98373][MODERATE REGULAR] mm/hugetlb: preserve mremap address delta when skipping page tables
@ 2026-10-08 1:31 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-08 1:31 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98373
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mm/hugetlb: preserve mremap address delta when skipping page tables
Commit: 7a96b0f657c8d799ea5b8e02fc9ec7cca0e6e7ff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a96b0f657c8d799ea5b8e02fc9ec7cca0e6e7ff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98373
Analysis date: Wed, 07 Oct 2026 21:31:38 -0400
ActionableScore: 2
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-2026-98373 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98373
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98373 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98373 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (legacy and Aegis reconciliation differ; DECISION: legacy MODERATE vs 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:L/I:L/A:H';CWE-682;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A logic error in move_hugetlb_page_tables can advance the destination address by a different offset than the source address when mremap skips an absent source page table entry or handles huge_pmd_unshare. If the source and destination offsets within their page tables differ, later page table operations can use an incorrect destination address. A reproducer reported a kernel panic on x86-64, resulting in local denial of service. For the CVSS the PR:L rating reflects that a local process must create and manipulate suitable hugetlb mappings through mremap. Reliable triggering also requires a specific hugepage mapping layout and page table state, so AC:H is appropriate. The paranoid score uses C:L I:L A:H as a manual review boundary because incorrect destination page table placement may affect mapping integrity, but privilege escalation is not confirmed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE READ OOB DANGER SIMPLEFIX LINUS MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Weak indirect corruption candidate. Incorrect `new_addr` advancement can cause subsequent hugetlb page-table operations to use a destination address that no longer corresponds to the source address.
* +1 Reliable kernel crash or strong DoS. The commit reports a reproducible kernel panic on x86-64.
Not awarded:
* No real UAF, stale post-free use, double release, refcount mutation, or RCU lifetime violation is established.
* No OOB read or write, arbitrary write, controlled reclaim, object replacement, callback influence, or directed page-table corruption is demonstrated.
* No confidentiality or integrity point is awarded. The patch demonstrates an invalid destination-address calculation and a panic, but not unauthorized access to another process memory or modification of protected state.
* No local-unprivileged trigger point is awarded. `mremap()` is normally a local user interface, but the complete required hugetlb mapping setup and allocation permissions are not established by the supplied context.
* No host-admin penalty is applied. A host-admin prerequisite is not positively established.
* No race or niche-subsystem penalty is applied. The defect is deterministic address arithmetic once the required mapping layout is reached, and hugetlb configuration uncertainty is not evidence for a negative score.
* No paranoid increment is justified. The same patch-supported evidence establishes a crash-capable invalid-state path, not an additional corruption or boundary-bypass primitive.
3. Reachability analysis
The trigger is local and involves `mremap()` on a hugetlb mapping with source and destination offsets that differ within their respective page-table ranges. The failure path also requires an absent source page-table entry or the `huge_pmd_unshare()` path.
A local process may be able to invoke `mremap()`, but the supplied patch does not establish that an ordinary unprivileged user can create and populate the required hugetlb mappings on a default system. Hugetlb page availability, hugetlbfs permissions, hugepage reservation, and memory-lock related policy can affect reachability. Therefore, host-admin requirement and namespace-scoped reachability remain UNKNOWN.
No network trigger, special hardware requirement, firmware dependency, or attacker-controlled timing race is established.
4. Primitive and severity interpretation
The exact primitive is incorrect destination virtual-address progression during hugetlb page-table movement. When the source page table is absent or is unshared, the old code advanced `old_addr` and `new_addr` independently to the end of their page-table regions. If their offsets differed, later operations could use an incorrectly advanced destination address.
This is not an active-object lifetime bug and does not involve fixed stale storage, a use-after-free, or a repeated lifetime/refcount mutation. The demonstrated consequence is a kernel panic, which supports local DoS.
The supplied evidence does not establish that the incorrect destination address reaches an attacker-selected mapping, overwrites a page-table entry outside the intended destination VMA, exposes another process memory, or bypasses a security boundary. Therefore the issue is classified as CLASS_C rather than CLASS_A or CLASS_B.
ImportantCandidate is NO because meaningful exploitation leverage beyond the demonstrated kernel crash remains unproven. AutoDowngradeAllowed is YES because the currently supported primitive is crash/DoS behavior without an established reusable corruption, ownership, authorization, or lifetime primitive.
5. One-sentence report phrase
Incorrect destination address advancement in hugetlb mremap page-table movement can cause later page-table operations to use a mismatched destination address and trigger a local kernel panic.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Verify the full `move_hugetlb_page_tables()` destination-range handling and reproduce the reported layout to determine whether the wrong `new_addr` can only cause a panic or can modify mappings outside the intended destination range.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mm/hugetlb: preserve mremap address delta when skipping page tables
Commit: 7a96b0f657c8d799ea5b8e02fc9ec7cca0e6e7ff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7a96b0f657c8d799ea5b8e02fc9ec7cca0e6e7ff
Commit description:
move_hugetlb_page_tables() optimizes mremap() by advancing to the last
entry in the page table when the source page table does not exist, either
initially or after unsharing a PMD table. The common loop increment then
steps to the first entry in the next page table.
However, the code advances both the source and destination addresses to
the last entries in their respective page tables, which is wrong. The
destination address must be advanced only by the same amount as the source
address.
If the source and destination offsets within their page tables differ, the
destination address can be advanced too far, causing follow-up issues.
Fix this by advancing the destination address by the source advance
distance.
With a reproducer, we were able to trigger a kernel panic on x86-64. With
this fix in place, we can no longer reproduce the issue.
Link: https://lore.kernel.org/[email protected]
Fixes: e95a985 ("hugetlb: skip to end of PT page mapping when pte not present")
Fixes: 4ddb4d9 ("hugetlb: do not update address in huge_pmd_unshare")
Signed-off-by: Jaewook You <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
Cc: Johan Hovold <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: <[email protected]>
Assisted-by: LLM
Signed-off-by: Greg Kroah-Hartman <[email protected]>
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=7a96b0f657c8d799ea5b8e02fc9ec7cca0e6e7ff
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98373 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98373
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:H
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: 2
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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