[CVE-2026-64519][LOW] NFSD: Fix infinite loop in layout state revocation [ Upstream

[CVE-2026-64519][LOW] NFSD: Fix infinite loop in layout state revocation [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64519
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: NFSD: Fix infinite loop in layout state revocation [ Upstream
Commit: d1fc00ec02e9deb3f8d2bd59caf938c554fbc576
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1fc00ec02e9deb3f8d2bd59caf938c554fbc576
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64519
Analysis date: Sat, 25 Jul 2026 10:42:56 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
NFSD layout state revocation can enter an infinite retry loop because layout stateids are closed without first being marked administratively revoked, causing a DoS in the revocation path but not indicating memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-64519 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64519

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.

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

CVE-2026-64519	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-703;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'NFSD layout state revocation can enter an infinite retry loop because the SC_TYPE_LAYOUT path closes a layout state without first marking the stateid as administratively revoked. The next lookup can therefore find the same layout stateid again and the revoker may hang indefinitely. For the CVSS the PR:L is used in the paranoid interpretation because an authenticated remote NFS client may be able to create or hold layout state, but a separate administrative revocation action is still needed. The issue is not a direct packet driven remote crash and it has high attack complexity with required user interaction in the paranoid model. Impact is denial of service against NFS state revocation or related server management paths. There is no evidence of UAF, OOB access, information disclosure, or privilege escalation in the provided patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	LOCK DANGER DISK SIMPLEFIX NETWORK  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel hang / DoS: +1. The revocation loop can repeatedly find the same layout stateid and hang indefinitely.
* Requires admin/root/CAP level operation in typical deployments: -2. The actual trigger is administrative NFS state revocation, not ordinary packet processing.
* Score floor applied: 0.

Paranoid signals:

* Reliable kernel hang / DoS: +1. The revoker can hang indefinitely.
* Broad server subsystem exposure: +1. NFSD is a common server subsystem when NFS server functionality is enabled.
* Requires admin/root/CAP level operation in typical deployments: -2. Reliable triggering still depends on an administrative revocation path.
* Availability impact realistic: +1. The hang can block NFS state revocation or related server management work.
* Remote client state influence: +1. A remote authenticated NFS or pNFS client may be able to create or hold layout state that later participates in the failing revocation path.
* No memory corruption, LPE, C, or I signals are supported.

## 3. Reachability analysis

A remote NFS client may influence the existence of layout state, but the patch does not show a directly packet-triggered crash or infinite loop. The reliable trigger appears to be an administrative layout state revocation operation on the NFSD server. Namespaces or containers do not materially lower the privilege requirement unless an untrusted actor is delegated meaningful NFS server administration. The path is relevant only on systems running NFSD with layout or pNFS functionality.

Call-site confidence: medium. The affected function and failure mode are visible, but wider administrative call paths are not fully included in the provided patch.

## 4. Severity interpretation

This behaves like a DoS-only logic bug rather than an Important-class kernel vulnerability. There is no evidence of UAF, OOB access, stale pointer reuse, double free, arbitrary write, information disclosure, or privilege escalation. The theoretical remote contribution is limited to preparing layout state, while realistic triggering requires an administrative revocation action.

## 5. One-sentence report phrase

NFSD layout state revocation can enter an infinite retry loop because layout stateids are closed without first being marked administratively revoked, causing a DoS in the revocation path but not indicating memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a DoS-only administrative-path logic bug with no supported memory corruption or security-boundary bypass primitive, so it can be handled as ordinary Moderate / Low-like unless product-specific NFSD administration is exposed to untrusted users.

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

Patch: NFSD: Fix infinite loop in layout state revocation [ Upstream
Commit: d1fc00ec02e9deb3f8d2bd59caf938c554fbc576
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d1fc00ec02e9deb3f8d2bd59caf938c554fbc576

Changed files:
  fs/nfsd/nfs4state.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=d1fc00ec02e9deb3f8d2bd59caf938c554fbc576

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

The original Linux kernel CVE announcement for CVE-2026-64519 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64519

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.8

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: 0
  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: NO
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).