[CVE-2026-43158][MODERATE 7.0] xfs: fix freemap adjustments when adding xattrs to leaf blocks [ Upstream

[CVE-2026-43158][MODERATE 7.0] xfs: fix freemap adjustments when adding xattrs to leaf blocks [ Upstream

[AL-KERNEL]

CVE: CVE-2026-43158
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfs: fix freemap adjustments when adding xattrs to leaf blocks [ Upstream
Commit: d08976725355b9d54d8332fce223fa281cc304a5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d08976725355b9d54d8332fce223fa281cc304a5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43158
Analysis date: Tue, 09 Jun 2026 18:04:45 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local user with permission to create extended attributes on XFS may be able to corrupt xattr leaf freemap accounting, causing metadata inconsistency and an XFS filesystem shutdown, with limited integrity concern but no demonstrated privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-43158 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43158

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.

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

CVE-2026-43158	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-682;CWE-617;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '5.8';DESCR 'An XFS xattr leaf block can become internally inconsistent because freemap entries are not always adjusted when the leaf entry array grows. A local user who can create extended attributes on an XFS filesystem may be able to construct xattr sizes and update sequences that make the freemap overlap the entry array. This can trigger an assertion and force an XFS filesystem shutdown, causing a local denial of service for that filesystem. For the CVSS the PR:L is used because reliable triggering requires local code execution and permission to modify xattrs on files, but does not normally require full administrator privileges. The issue is not network reachable. Impact is mainly availability loss, with limited integrity concern due to inconsistent filesystem metadata and no supported evidence of privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB DISK LINUS KPANIC 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local user with write permission on an XFS filesystem can plausibly trigger the path through repeated `setxattr` operations with specific xattr sizes and update sequences.

* Filesystem/storage metadata corruption reachable by an unprivileged local user: +1
  The bug makes XFS xattr leaf block freemap metadata overlap the leaf entry array.

* Reliable kernel crash / strong DoS: +1
  The described failure triggers an XFS assertion and filesystem shutdown.

* Important filesystem/storage path: +1
  This affects XFS metadata handling, specifically extended attribute leaf block accounting.

* Integrity impact plausible: +1 in paranoid score
  The issue is metadata inconsistency rather than arbitrary write, but it affects persistent filesystem metadata state enough to justify limited integrity concern.

* Corruption primitive highly constrained or metadata-only: -1
  There is no evidence of attacker-controlled kernel memory overwrite, UAF, arbitrary write, type confusion, or privilege escalation primitive.

## 3. Reachability analysis

The bug is locally reachable by a user who can create or modify extended attributes on files in an affected XFS filesystem. It does not require root in the generic case, only normal filesystem write and xattr permissions.

The issue is not network reachable. Containers or namespaces may matter if an untrusted container has write access to a host-backed XFS filesystem or shared persistent volume, but namespaces do not by themselves create the vulnerable condition.

The affected subsystem is common and broadly deployed, since XFS is a major Linux filesystem. Triggering requires a specific xattr leaf freemap state, so this is not a trivial one-shot crash, but the commit indicates fsstress can reproduce it.

## 4. Severity interpretation

This behaves more like an actionable Moderate filesystem integrity and availability issue than an Important kernel memory corruption vulnerability.

Theoretical impact is stronger than a simple assertion because the underlying problem is inconsistent filesystem metadata. Realistic evidence supports filesystem shutdown and local DoS, not LPE. There is no demonstrated UAF, arbitrary write, page-cache corruption, or attacker-controlled overwrite primitive.

## 5. One-sentence report phrase

A local user with permission to create extended attributes on XFS may be able to corrupt xattr leaf freemap accounting, causing metadata inconsistency and an XFS filesystem shutdown, with limited integrity concern but no demonstrated privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is justified because this is filesystem metadata corruption reachable from local xattr operations and can force XFS shutdown. It should not be auto-closed as a low-risk assertion-only issue, even though the current evidence does not support Important-class memory corruption or LPE.

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

Patch: xfs: fix freemap adjustments when adding xattrs to leaf blocks [ Upstream
Commit: d08976725355b9d54d8332fce223fa281cc304a5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d08976725355b9d54d8332fce223fa281cc304a5

Changed files:
  fs/xfs/libxfs/xfs_attr_leaf.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=d08976725355b9d54d8332fce223fa281cc304a5

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

The original Linux kernel CVE announcement for CVE-2026-43158 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43158

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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).