[CVE-2026-53244][MODERATE 7.0] VFS: fix possible failure to unlock in nfsd4_create_file() [ Upstream

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

CVE: CVE-2026-53244
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: VFS: fix possible failure to unlock in nfsd4_create_file() [ Upstream
Commit: ee1f40759a50b1800c98c1c369afd5b3e44ad987
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee1f40759a50b1800c98c1c369afd5b3e44ad987
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53244
Analysis date: Thu, 25 Jun 2026 20:19:05 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A network-reachable NFSD create error path can leave a parent directory locked when atomic_open fails, causing denial of service for later operations on the affected export, with no clear evidence of memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53244 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53244

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-2026-53244	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;CWE-755;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'A lock handling flaw in the VFS create path can be reached through nfsd4_create_file when an exported filesystem uses atomic_open and that operation returns an error. In this error path atomic_open can drop the dentry reference while the NFS server side caller still needs a valid dentry to complete end_creating and unlock the parent directory. The result is a stuck parent directory lock and a denial of service for later operations on the affected export or directory. For the CVSS the PR:N is used in the paranoid network interpretation because a reachable NFS client may only need access to an exported share that permits create attempts. The base score uses PR:L because reliable triggering normally requires valid NFS credentials or write permission on the export. The issue is network reachable through NFSD but requires a specific exported filesystem behavior and an error from atomic_open, so AC:H is appropriate. Impact is availability only. No concrete UAF, OOB access, information leak, or privilege escalation primitive is visible from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-53244  SKIP The Fixes patch not applied yet, so unlikely that actual: 64a989dbd144e0622371396461b11335459692d2 YES  NO NO unknown 	MAYBE	DISK LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	-	-	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

* Remote reachable / network-triggerable: +2
  Reachable through NFSD if an attacker can send NFS create operations to an exported filesystem.

* Reliable kernel crash / strong DoS: +1
  The failure mode is a missed parent directory unlock, which can stall later operations on the affected directory or export.

* Important filesystem/storage path: +1
  The bug is in the VFS/NFSD create path and affects filesystem locking semantics.

* Availability impact realistic: +1 paranoid only
  The stuck parent lock may persist and affect future operations until recovery or reboot, so the paranoid score counts stronger availability impact.

No memory corruption signal is counted. The patch shows dentry lifetime and unlock correctness, but not UAF reclaim, OOB write, arbitrary write, information leak, or privilege escalation.

## 3. Reachability analysis

A remote NFS client can potentially trigger the bug by issuing create operations against an NFSD export backed by a filesystem using atomic_open or atomic_create, when that operation returns an error. Reliable triggering normally requires valid NFS access and create permission on the export, but the paranoid interpretation treats this as PR:N in CVSS terms because the attacker only needs network reachability to an exposed NFS service that permits the operation. This is not a default local-only interface, but NFSD is commonly deployed in server environments. The condition is specific, so exploitability is not trivial.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an Important memory-corruption vulnerability. The realistic impact is availability loss through a lock leak or deadlock-like condition in the NFS create path. There is no demonstrated confidentiality or integrity primitive. Theoretical escalation is not supported by the patch context, so the score should not be raised into Important solely based on dentry reference handling.

## 5. One-sentence report phrase

A network-reachable NFSD create error path can leave a parent directory locked when atomic_open fails, causing denial of service for later operations on the affected export, with no clear evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is network reachable through NFSD and can cause persistent availability impact, even though the apparent vulnerability class is DoS-only and not memory corruption.

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

Patch: VFS: fix possible failure to unlock in nfsd4_create_file() [ Upstream
Commit: ee1f40759a50b1800c98c1c369afd5b3e44ad987
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee1f40759a50b1800c98c1c369afd5b3e44ad987

Changed files:
  fs/namei.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=ee1f40759a50b1800c98c1c369afd5b3e44ad987

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

The original Linux kernel CVE announcement for CVE-2026-53244 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53244

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:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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).