[CVE-2026-90262][LOW] btrfs: retry verity reads for not-uptodate Merkle folios [ Upstream

[CVE-2026-90262][LOW] btrfs: retry verity reads for not-uptodate Merkle folios [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90262
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: YES
Patch: btrfs: retry verity reads for not-uptodate Merkle folios [ Upstream
Commit: 90e9eae1b5907fa36620ffb7f4f1a4afa9333427
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=90e9eae1b5907fa36620ffb7f4f1a4afa9333427
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90262
Analysis date: Fri, 18 Sep 2026 02:00:35 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A transient Btrfs fs-verity read failure can leave a Merkle folio not uptodate or locked, causing persistent EIO responses or blocked readers without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-90262 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90262

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: LOW
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-2026-90262	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90262 CHECK WITH IMPACT FROM ORIG NN NONE	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:N/A:H';CWE-667;CWE-755;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A transient Btrfs verity Merkle tree read failure can leave a folio not uptodate in the page cache. Later readers can find the same folio and receive persistent EIO errors instead of retrying the read. An error from read_key_bytes can also leave the folio locked, which may block later readers waiting for that folio. For the CVSS the PR:L value is used because a local process must access the affected fs verity file, while reliable triggering also depends on a transient storage read failure or a similar exceptional condition. The issue is not directly network reachable. Impact is normally limited to availability of the affected file or operation, although blocked access to a critical verity protected file could cause broader service disruption. There is no supported UAF, OOB access, information leak, or write primitive, so confidentiality and integrity remain unaffected.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-90262 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	LOCK DISK SIMPLEFIX SKIP KPANIC MEMORY 	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

## 2. Signal breakdown

Positive signals:

* +1 Important filesystem or storage path. The defect affects Btrfs fs-verity Merkle-tree reads and can prevent successful verification and access to affected files.
* +1 Availability impact. A transient read failure can become persistent EIO, while the missing `folio_unlock()` can leave later readers blocked on the affected folio.

Negative signals:

* No negative points. Host-admin privilege, rare hardware, a difficult race, and an unusually inaccessible configuration are not positively established.

Important non-awarded signals:

* No UAF, stale post-lifetime reference, OOB access, double release, or refcount corruption is established.
* No reliable kernel crash, filesystem shutdown, or host-wide DoS is demonstrated.
* No arbitrary write, controlled reclaim, information disclosure, integrity violation, or privilege-escalation primitive is established.
* No remote reachability or security-boundary bypass is established.
* The broader disruption of a service that depends on a critical verity file is plausible, but it is not an independent primitive and does not justify an additional paranoid point.

## 3. Reachability analysis

A local process reading the affected Btrfs fs-verity file can encounter the sticky error or wait on the locked folio. However, reliable triggering also requires a preceding failure from `read_key_bytes()` or another transient storage-read failure, and the supplied evidence does not show that an ordinary user can deliberately induce that condition.

The complete privilege boundary is therefore unresolved, so `HostAdminRequired=UNKNOWN`. No namespace capability is relevant or established. Btrfs and fs-verity must already be in use, but no special hardware, boot mode, or timing race is required by the patch.

## 4. Primitive and severity interpretation

The exact primitive is incorrect error recovery and folio-lock handling. A not-uptodate folio remains cached and is treated as a permanent error, while one failure path drops the folio reference without first unlocking the folio.

This is not a stale-storage or active-object UAF. There is no first lifetime-ending operation followed by use of a dangling reference, and no repeated release or refcount mutation exists. The demonstrated consequences are persistent EIO and blocked readers, making this `CLASS_C`.

`ImportantCandidate=NO` because no corruption, ownership violation, authorization bypass, or meaningful exploitation leverage beyond availability loss is present. `AutoDowngradeAllowed=YES` because the impact is constrained to error persistence and lock-based blocking, with no unresolved security primitive.

Likely operational severity is Low to ordinary Moderate, depending on whether a critical service relies on the affected verity-protected file.

## 5. One-sentence report phrase

A transient Btrfs fs-verity read failure can leave a Merkle folio not uptodate or locked, causing persistent EIO responses or blocked readers without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a constrained availability defect with no UAF, corruption primitive, disclosure, authorization bypass, or credible privilege-escalation path.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: btrfs: retry verity reads for not-uptodate Merkle folios [ Upstream
Commit: 90e9eae1b5907fa36620ffb7f4f1a4afa9333427
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=90e9eae1b5907fa36620ffb7f4f1a4afa9333427

Changed files:
  fs/btrfs/verity.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=90e9eae1b5907fa36620ffb7f4f1a4afa9333427

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

The original Linux kernel CVE announcement for CVE-2026-90262 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90262

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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: LOW
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): LOW

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).