[CVE-2026-45974][MODERATE REGULAR] btrfs: fix invalid leaf access in btrfs_quota_enable() if ref key not found [ Upstream

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

CVE: CVE-2026-45974
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: btrfs: fix invalid leaf access in btrfs_quota_enable() if ref key not found [ Upstream
Commit: 023545e272f369d487e6a986c1e321c6e04be1da
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=023545e272f369d487e6a986c1e321c6e04be1da
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45974
Analysis date: Wed, 27 May 2026 09:02:02 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-45974 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45974

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.

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

CVE-2026-45974	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';CWE-754;CWE-703;CWE-125;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.2';DESCR 'btrfs_quota_enable could continue scanning after btrfs_search_slot_for_read indicated that the search reached the end of the tree and the current path was no longer valid. A later btrfs_next_item call could then operate on an invalid path or leaf while enabling qgroups, which may lead to a kernel crash or incorrect filesystem metadata handling. For the CVSS the PR:H is used because enabling Btrfs quotas normally requires administrative filesystem control such as CAP_SYS_ADMIN. The issue is not network reachable and is triggered through a local filesystem management operation. Impact is mainly availability, with low confidentiality and integrity concern only in the paranoid interpretation because the bug is an invalid metadata tree access rather than a proven memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)	YES	DISK SIMPLEFIX SKIP  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

2. Signal breakdown
* Reliable kernel crash / strong DoS: +1. Continuing with an invalid Btrfs path can lead to invalid leaf access and likely crash or abort in filesystem code.
* Important filesystem/storage path: +1. The bug is in Btrfs qgroup quota enable logic and touches filesystem tree metadata traversal.
* Availability impact realistic: +1. Invalid metadata path access during quota enable can disrupt filesystem management and may crash the kernel or fail the operation.
* Integrity impact plausible in paranoid scoring: +1. The affected code walks filesystem metadata, so incorrect traversal has a limited theoretical metadata integrity concern, although no write corruption primitive is shown.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Enabling Btrfs quotas is an administrative filesystem operation.
* Weak corruption only: +0. The patch shows invalid path or leaf access, but not UAF reclaim, OOB write, arbitrary write, page-cache corruption, or controlled overwrite.
* No remote reachability: +0. This is not packet-triggered or network exposed.

3. Reachability analysis
The bug is triggered through local Btrfs quota enable operations. In normal deployments this requires CAP_SYS_ADMIN or equivalent administrative filesystem control. User namespaces or containers usually do not make this directly reachable against the host filesystem unless a privileged container or management service is allowed to operate on the host Btrfs mount. The path is not default-triggered by ordinary file I/O and is not remotely reachable. Realistic exploitation is mainly an admin-triggered crash or filesystem management failure.

4. Severity interpretation
This behaves like a low to borderline Moderate filesystem bug rather than an Important-class vulnerability. The theoretical concern is invalid metadata tree access in an important filesystem subsystem. The realistic evidence supports DoS or operation failure, not privilege escalation or controlled memory corruption. Because filesystem metadata paths can have non-obvious side effects, manual review is reasonable, but the CAP_SYS_ADMIN requirement keeps practical urgency low.

5. One-sentence report phrase
Btrfs quota enable could continue after reaching the end of a metadata tree search and operate on an invalid path or leaf, causing a local administrative DoS risk during qgroup setup.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED
The bug affects an important filesystem metadata traversal path, but it requires administrative Btrfs quota management and does not show a strong memory corruption or LPE primitive.

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

Patch: btrfs: fix invalid leaf access in btrfs_quota_enable() if ref key not found [ Upstream
Commit: 023545e272f369d487e6a986c1e321c6e04be1da
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=023545e272f369d487e6a986c1e321c6e04be1da

Changed files:
  fs/btrfs/qgroup.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=023545e272f369d487e6a986c1e321c6e04be1da

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

The original Linux kernel CVE announcement for CVE-2026-45974 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45974

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.2

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: 1
  Paranoid ActionableScore: 3

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).