[CVE-2026-80893][MODERATE 7.0] mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() [ Upstream

[CVE-2026-80893][MODERATE 7.0] mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-80893
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() [ Upstream
Commit: f1b1311c0352873137768bac5a126e491271a747
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f1b1311c0352873137768bac5a126e491271a747
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80893
Analysis date: Fri, 04 Sep 2026 15:38:42 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local hugetlb fork path can corrupt migration or hwpoison swap entries because a present PTE uffd-wp clearing helper is applied to swap-style entries, potentially causing denial of service and requiring manual review for memory-management integrity impact.

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

The original Linux kernel CVE announcement for CVE-2026-80893 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80893

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-80893	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80893 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:H/I:H/A:H';CWE-682;*CWE-664;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A hugetlb swap entry corruption can occur during fork() because copy_hugetlb_page_range() used huge_pte_clear_uffd_wp() on migration and hwpoison entries. That helper clears the present PTE bit position, while swap entries store uffd-wp state elsewhere, so the operation can corrupt the encoded swap offset or PFN copied into the child process. No userfaultfd registration is required because the condition depends on the child VMA not being uffd-wp registered and on an in-flight hugetlb migration entry or a hwpoison entry. For the CVSS the PR:L is used for the paranoid score because a local user context can trigger fork() on its own mappings, although reliable triggering depends on hugetlb availability and migration or hwpoison timing. The issue is not network reachable. Impact is at least a local denial of service or corrupted memory mapping state and in worst case may allow confidentiality or integrity impact due to memory-management entry corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	DANGER INIT LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Local unprivileged trigger: +1**
  A local process can trigger `fork()` on its own hugetlb mappings. No userfaultfd registration is required, but hugetlb availability is still a practical condition.

* **Strong attacker-influenced semantic reinterpretation primitive: +2**
  The bug applies a present-PTE uffd-wp clearing helper to swap-like migration and hwpoison entries. This causes the same encoded bits to be interpreted under the wrong layout and corrupts the swap offset or PFN payload.

* **Memory corruption, weak/indirect corruption candidate: +1**
  The corrupted object is a memory-management entry rather than a simple warning or resource leak. However, the patch does not show an arbitrary write, attacker-controlled reclaim, or controlled object replacement.

* **Integrity impact plausible: +1**
  A corrupted migration entry can be re-encoded by paths such as `hugetlb_change_protection()`, propagating an incorrect PFN or offset.

* **Availability impact realistic: +1**
  Corrupt hugetlb migration or hwpoison entries can plausibly cause process failure, mapping corruption, or kernel-side MM faults.

Negative signals:

* **Hard or unreliable race / special timing required: -1**
  Reliable triggering requires a fork while a hugetlb migration entry or hwpoison entry is present.

Paranoid additional signals:

* **Weak LPE concern: +1**
  The primitive affects page-table or swap-entry semantics. It is not a proven LPE, but MM entry corruption can be security-sensitive and deserves manual review.

* **Confidentiality impact plausible: +1**
  A corrupted PFN or offset in a memory-management entry may theoretically expose unintended memory mappings, although the patch does not demonstrate a direct disclosure primitive.

Paranoid result: **7**

## 3. Reachability analysis

The bug is **local-only** and not network reachable. The most relevant trigger is a local process using hugetlb memory and calling `fork()` while the source mapping contains an in-flight hugetlb migration entry or a hwpoison entry. `MADV_HWPOISON` itself is privileged, but the commit explicitly states that userfaultfd is not required and that a plain `fork()` can corrupt the copied child entry if the timing condition already exists.

Namespaces and containers may matter if hugetlb pages are delegated to workloads. A fully unprivileged user may not always have access to hugetlb pages, but in systems where hugetlb is exposed to applications, databases, VMs, or containers, the effective trigger can be closer to **PR:L** than **PR:H**. The path is not a default everyday memory path, but hugetlb is common enough in performance-sensitive workloads that this should not be auto-closed as a niche-only correctness issue.

Call-site confidence: **high**, because the patch and commit message identify the exact affected call path in `copy_hugetlb_page_range()` and describe downstream propagation through `hugetlb_change_protection()`.

## 4. Severity interpretation

This behaves more like an **Actionable Moderate with Strong Important candidate properties**, not an ordinary Moderate. The conservative interpretation is that the issue causes local hugetlb swap-entry corruption with realistic DoS and plausible integrity impact. The paranoid interpretation is stronger because the corruption affects memory-management metadata containing PFN or offset information, and such bugs can sometimes become privilege or isolation issues even when the initial report only demonstrates corrupted state.

Theoretical LPE is not proven. There is no demonstrated arbitrary write, object reclaim, callback control, or type confusion. Still, the primitive is more serious than a pure NULL dereference or warning because it corrupts MM entry encoding and may propagate through later page-table operations.

## 5. One-sentence report phrase

A local hugetlb fork path can corrupt migration or hwpoison swap entries because a present PTE uffd-wp clearing helper is applied to swap-style entries, potentially causing denial of service and requiring manual review for memory-management integrity impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is not a simple DoS-only bug. The patch fixes corruption of encoded hugetlb migration or hwpoison entries, including PFN or swap-offset payload corruption, with a plausible path to propagated MM state corruption.

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

Patch: mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() [ Upstream
Commit: f1b1311c0352873137768bac5a126e491271a747
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f1b1311c0352873137768bac5a126e491271a747

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=f1b1311c0352873137768bac5a126e491271a747

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

The original Linux kernel CVE announcement for CVE-2026-80893 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80893

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: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: 5
  Paranoid ActionableScore: 7

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).