[CVE-2026-92502][MODERATE REGULAR] ext4: clear stale xarray tags on folios skipped during writeback [ Upstream

[CVE-2026-92502][MODERATE REGULAR] ext4: clear stale xarray tags on folios skipped during writeback [ Upstream

[AL-KERNEL]

CVE: CVE-2026-92502
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ext4: clear stale xarray tags on folios skipped during writeback [ Upstream
Commit: f82a4929d0ef7ddf254c1c295ec1dfd24094f2de
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f82a4929d0ef7ddf254c1c295ec1dfd24094f2de
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92502
Analysis date: Fri, 18 Sep 2026 04:07:33 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-92502 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92502

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-2026-92502	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-92502 CHECK WITH IMPACT FROM ORIG NN LOW	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:L/A:H';CWE-362;*CWE-664;CWE-459;Other CVSS 'AV:L/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'In ext4 data journal mode, clean folios can keep stale xarray dirty or towrite tags after journal checkpointing. Writeback may later select these folios even though PG_dirty is already clear, skip the normal writeback path, and leave the stale tags in place. During reboot or read only remount this can make ext4 enter writeback and attempt to start a journal transaction after the superblock became read only, producing warnings and a possible data loss condition. For the CVSS the PR:L is used because a local user may be able to create the write workload that leaves stale tagged folios, while the final trigger often depends on reboot or remount timing. The issue is not network reachable and does not show a UAF, OOB access, or arbitrary write primitive. Impact is mainly availability degradation and limited integrity risk from possible filesystem data loss under non default data journal conditions.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	DISK HARDWARE LINUS BOOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap was applied.

2. Signal breakdown

Conservative positive signals:

* +1 Important filesystem/storage path. The bug is in ext4 writeback and data journaling behavior, involving page-cache xarray tags and journal checkpoint interaction.
* +1 Integrity plausible. The commit reports an ext4 warning that data will be lost after the stale tag condition is hit during read-only remount or reboot.
* +1 Filesystem/page-cache state inconsistency. Clean folios can retain PAGECACHE_TAG_DIRTY and PAGECACHE_TAG_TOWRITE, causing writeback to process stale metadata state even though PG_dirty is clear.

Paranoid additional signal:

* +1 Availability degradation plausible. The issue can repeatedly drive writeback into an invalid read-only-remount state and produce WARN paths during reboot/remount, which may disrupt shutdown or filesystem cleanup behavior.

Non-awarded signals:

* No RealUAF. The patch does not establish freed-object reuse, stale lifetime object dereference, double free, or refcount mutation after free.
* No controlled reclaim, arbitrary write, OOB access, or type confusion is demonstrated.
* No confidentiality impact is awarded. There is no disclosure path.
* No strong integrity primitive is awarded. The evidence supports possible data loss, not attacker-directed modification of another file or metadata object.
* No remote reachability is established.
* No local unprivileged trigger bonus is awarded conservatively because the full manifestation depends on ext4 data=journal plus remount read-only or reboot timing.
* No race penalty is applied. The issue is timing-dependent but reported as frequent under load, not a narrow one-shot race.
* No rare-subsystem penalty is applied. data=journal is non-default, but it is a supported ext4 mode and not enough by itself to classify the affected path as rare and unreachable.

3. Reachability analysis

The condition requires ext4 mounted in data=journal mode. The reproduction uses a local write-heavy workload followed by reboot, with the superblock being remounted read-only while writeback still sees stale xarray tags.

A local user may be able to create the heavy write workload if they can write to the affected filesystem. However, enabling data=journal usually requires administrator configuration, and the final trigger often depends on reboot or read-only remount timing. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

NamespaceScopedPrivilege is NO because this is a filesystem/writeback issue, not a namespace-scoped capability path.

No network trigger is present. No special hardware is required. The race/timing aspect appears reproducible under load, but not deterministically attacker-controlled from the supplied evidence.

4. Primitive and severity interpretation

The exact primitive is stale page-cache xarray tag state on clean folios in ext4 data=journal mode. PAGECACHE_TAG_DIRTY and PAGECACHE_TAG_TOWRITE can remain set after PG_dirty is clear, causing writeback to revisit clean folios and miss the normal tag-clearing path.

This is not an active structured UAF and not fixed stale storage after free. It is a filesystem metadata/state-consistency bug in the writeback path.

PrimitiveClass is CLASS_C because the demonstrated behavior is invalid stale writeback state, WARN_ON during read-only remount, and possible data loss warning. It does not establish an independently useful memory corruption or authorization primitive.

Demonstrated consequence: warnings during reboot/remount and possible filesystem data loss condition.

Speculative consequence: broader data-loss impact if stale tags persist across stressful writeback/remount timing. There is no evidence of privilege escalation, arbitrary write, or cross-file ownership/COW bypass.

ImportantCandidate is NO because no Class A or strong unresolved Class B primitive is present. ManualReview is RECOMMENDED because ext4 writeback plus possible data loss is operationally important and should not be treated as a trivial warning-only bug. AutoDowngradeAllowed is YES because there is no UAF, memory corruption, authorization bypass, or unresolved Important-grade primitive.

Likely operational severity: borderline Moderate. It is more important than a cosmetic WARN, but below Important without stronger evidence of attacker-directed corruption or reliable unprivileged triggering.

5. One-sentence report phrase

In ext4 data journal mode, stale xarray dirty or towrite tags on clean folios can make writeback run during read-only remount or reboot and produce warnings with possible data loss, but no UAF, arbitrary write, or privilege escalation primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: ext4 writeback and journaling data-loss symptoms are security-relevant enough for human triage, but the patch supports stale metadata state and possible data loss rather than memory corruption or a strong exploitation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: ext4: clear stale xarray tags on folios skipped during writeback [ Upstream
Commit: f82a4929d0ef7ddf254c1c295ec1dfd24094f2de
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f82a4929d0ef7ddf254c1c295ec1dfd24094f2de

Changed files:
  fs/ext4/inode.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=f82a4929d0ef7ddf254c1c295ec1dfd24094f2de

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

The original Linux kernel CVE announcement for CVE-2026-92502 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92502

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:R/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.3

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: 3
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).