[CVE-2026-68086][MODERATE 7.0] mm/khugepaged: write all dirty file folios when collapsing [There is no upstream commit, as this code was removed by upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-68086
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mm/khugepaged: write all dirty file folios when collapsing [There is no upstream commit, as this code was removed by upstream
Commit: 2dfe9f5c91d0963058f8a5e46e1c2a908382cc46
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dfe9f5c91d0963058f8a5e46e1c2a908382cc46
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68086
Analysis date: Mon, 10 Aug 2026 12:45:08 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local page-cache data-loss bug in khugepaged file THP collapse can allow dirty file folios from previous writers to be discarded during a later writable open, causing persistent file integrity loss under a specific ordering of write, collapse, and reopen operations.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68086 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68086

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
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CVE-2026-68086	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:H/A:H';CWE-221;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.3';DESCR 'File THP collapse in khugepaged can coexist with dirty file folios left by previous writers. A local process may trigger the edge case by writing a file, closing it, causing MADV_COLLAPSE or file THP collapse on the mapping, and later opening the file writable so page cache truncation can discard dirty folios. For the CVSS the PR:L is used because reliable triggering requires local code execution and access to the affected file or mapping, but does not normally require full administrator privileges. The issue is not network reachable and is not a kernel memory corruption primitive. Impact is data loss with integrity impact and possible availability impact for affected file contents.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB INIT LINUS KPANIC MEMORY  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative scoring:

* Local unprivileged trigger: +1. A local user with access to the file or mapping can plausibly participate in the sequence involving write, close, MADV_COLLAPSE or file THP collapse, and later writable open.
* Page-cache data-loss / weak page-cache corruption concern: +1. The bug affects dirty file-backed folios in the page cache and can cause them to be discarded instead of written back.
* Important filesystem/storage path: +1. The affected logic is in khugepaged file THP collapse and interacts with page cache, writeback, and writable file open semantics.
* Integrity impact plausible: +1. Dirty file contents can be lost, so stored data integrity can be affected.
* Availability impact realistic: +1. Data loss can affect service availability or correctness of applications relying on the file contents.
* Hard edge case / special ordering required: -1. The trigger requires a specific sequence with previous dirty folios, file THP collapse, no active writable opener, and later writable open.

Paranoid adjustment:

* Page-cache corruption or file-backed data corruption: +2 instead of +1. The affected object is dirty file-backed cache state, and the result is persistent data loss rather than a transient warning or crash.

Not counted:

* No remote reachability.
* No generic kernel memory corruption.
* No UAF, double-free, OOB write, arbitrary write, type confusion, or demonstrated LPE primitive.
* No Dirty-Pipe-like attacker-controlled write into protected file-backed pages. This is loss of dirty data, not injection of attacker-controlled data into another object.

## 3. Reachability analysis

The bug is locally reachable through file and memory-management operations, but only under a narrow ordering of events. A process must create dirty file folios, close the writable file, allow or request file THP collapse, and then trigger a later writable open that causes page-cache truncation while dirty folios can be discarded.

This does not appear network reachable by itself. Containers or namespaces may matter if an untrusted workload can access affected files and use MADV_COLLAPSE or otherwise induce file THP collapse, but the core trigger is still local. The path is in mm/page-cache behavior, so it is security-relevant even though the exact configuration is specialized.

## 4. Severity interpretation

This is not an Important-class memory-corruption vulnerability based on the provided patch. It behaves more like an actionable Moderate issue because it can cause real file data loss in a core storage/page-cache path.

Theoretical escalation beyond data loss is not supported by the patch. Realistic impact is integrity loss and possible availability impact for affected file contents. Because page-cache and writeback semantics are involved, and because persistent data loss can be operationally serious, it should not be auto-closed as an ordinary low-risk correctness bug.

## 5. One-sentence report phrase

A local page-cache data-loss bug in khugepaged file THP collapse can allow dirty file folios from previous writers to be discarded during a later writable open, causing persistent file integrity loss under a specific ordering of write, collapse, and reopen operations.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the issue affects dirty file-backed page-cache state and can cause persistent data loss, even though it does not show a kernel memory-corruption or privilege-escalation primitive.

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

Patch: mm/khugepaged: write all dirty file folios when collapsing [There is no upstream commit, as this code was removed by upstream
Commit: 2dfe9f5c91d0963058f8a5e46e1c2a908382cc46
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2dfe9f5c91d0963058f8a5e46e1c2a908382cc46

Changed files:
  mm/khugepaged.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=2dfe9f5c91d0963058f8a5e46e1c2a908382cc46

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

The original Linux kernel CVE announcement for CVE-2026-68086 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68086

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:H/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H
  The Best / paranoid CVSS score: 6.3

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).