[CVE-2026-89694][MODERATE 7.0] nfsd: check client ownership when cancelling a copy-notify stateid

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

CVE: CVE-2026-89694
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nfsd: check client ownership when cancelling a copy-notify stateid
Commit: b1eca07303594ca27f5dc360a6946bd7e1f5b04c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1eca07303594ca27f5dc360a6946bd7e1f5b04c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89694
Analysis date: Fri, 11 Sep 2026 23:15:50 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
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-2026-89694 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89694

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-2026-89694	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89694 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H';CWE-862;CWE-863;CWE-639;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '7.1';DESCR 'An authorization flaw in nfsd OFFLOAD_CANCEL allowed an authenticated NFSv4.2 client to cancel and free another clients copy notify stateid. The state lookup used a cyclic and guessable so_id, while the embedded clientid was a fixed per net value, so ownership of the copy notify state was not enforced before deletion. For the CVSS the PR:L is used because the attacker must be an authenticated NFSv4.2 client with network access to the NFS server, but does not need administrative privileges on the victim. The issue is network reachable through the NFSv4.2 control path and does not require local code execution on the server. Impact is mainly integrity and availability: an attacker can disrupt another clients server to server copy workflow by invalidating its state, causing operation failure or service degradation for that feature. There is no concrete evidence of kernel memory corruption, information disclosure, or privilege escalation from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	DISK UAF NETWORK LINUS KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 6
* Paranoid score: 6. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2 Concrete authorization decision bypass. The OFFLOAD_CANCEL path freed copy-notify state without verifying that the requesting NFSv4.2 client was the creator.
* +2 Remote reachable network control path. An authenticated NFSv4.2 client can reach the affected nfsd operation over the network.
* +1 Integrity impact. The attacker can cause unauthorized deletion of another client copy-notify state.
* Paranoid only +1 Availability impact. Because the stateid component is cyclic and guessable, repeated cancellation attempts could disrupt another clients server-side copy workflow or degrade that NFS feature.

Non-awarded signals:

* RealUAF not awarded. The patch shows unauthorized freeing of another clients live state, not a stale post-lifetime use by the kernel.
* Memory corruption not awarded. No UAF, OOB write, arbitrary write, or controlled reclaim is established.
* Confidentiality not awarded. No disclosure path or protected data read is shown.
* LPE not awarded. No privilege escalation path is established.
* Sensitive FD or credential theft not awarded. No downstream protected resource theft is shown.
* Extra availability not double-counted in the conservative score because the main state deletion and operation disruption overlap.
* Concrete repeated release/refcount not awarded. There is no visible first release that can end lifetime followed by a second lifetime mutation through the same dangling reference.

3. Reachability analysis

The attacker is an authenticated NFSv4.2 client with network access to the vulnerable NFS server. Host administrator privileges on the victim are not required. The relevant privilege is protocol-level authentication and access to the NFSv4.2 control path, not local code execution on the server.

The complete trigger does not depend on Linux namespaces or namespace-scoped capabilities. NamespaceScopedPrivilege is therefore NO. The vulnerable feature requires an NFS server exposing the relevant NFSv4.2 copy-notify or server-side copy functionality, which is prior service configuration but not host-admin privilege for the attacker once exposed.

The state lookup is materially attacker-relevant because so_id is cyclic and guessable, while the embedded clientid is fixed per network namespace. No hard race or special hardware prerequisite is established.

4. Primitive and severity interpretation

The exact primitive is a network-reachable authorization and ownership check bypass in nfsd state management. The missing check allowed a client to cancel and free a copy-notify stateid owned by another client.

This is not an ordinary kernel memory corruption primitive. It is a security-boundary violation between authenticated NFS clients sharing the same server. The demonstrated consequence is unauthorized invalidation of another clients copy-notify state, causing operation failure or degradation of server-side copy behavior.

PrimitiveClass is CLASS_A because the patch restores a mandatory ownership check that changes an incorrect ALLOW behavior back to DENY with nfserr_bad_stateid. ImportantCandidate is YES because this is a network-reachable cross-client authorization bypass in a server subsystem. AutoDowngradeAllowed is NO because automatically closing it as ordinary low-impact DoS would lose the established security-boundary primitive.

Operationally, this is best treated as Actionable Moderate with Strong Important review potential, rather than a crash-only or resource-only bug.

5. One-sentence report phrase

An authenticated NFSv4.2 client could exploit a missing ownership check in nfsd OFFLOAD_CANCEL to cancel another clients copy-notify stateid, causing unauthorized state deletion and disruption of server-side copy operations.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable authorization bypass affecting cross-client NFS server state, with guessable state identifiers and possible integrity and availability impact.

7. Call-site confidence

Call-site confidence: high

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

Patch: nfsd: check client ownership when cancelling a copy-notify stateid
Commit: b1eca07303594ca27f5dc360a6946bd7e1f5b04c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b1eca07303594ca27f5dc360a6946bd7e1f5b04c

Commit description:

On the OFFLOAD_CANCEL path (clp != NULL), manage_cpntf_state() freed the
target cpntf state without checking ownership. The lookup key
st->si_opaque.so_id is allocated cyclically (guessable) and the embedded
clientid is the fixed per-net nn->s2s_cp_cl_id, so any authenticated
NFSv4.2 client could cancel and free another client's copy-notify
stateid.

Compare the creating clientid recorded in state->cp_p_clid against the
requesting client's cl_clientid and return nfserr_bad_stateid on a
mismatch instead of freeing the entry.

Fixes: ce0887a ("NFSD add nfs4 inter ssc to nfsd4_copy")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260710-nfsd-testing-v3-5-a0ff7db6aa3e@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=b1eca07303594ca27f5dc360a6946bd7e1f5b04c

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

The original Linux kernel CVE announcement for CVE-2026-89694 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89694

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:L/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 7.1

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: 5
  Paranoid ActionableScore: 6

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).