[CVE-2026-89669][IMPORTANT] nfsd: initialize copy-notify stateid before publishing it

[CVE-2026-89669][IMPORTANT] nfsd: initialize copy-notify stateid before publishing it

[AL-KERNEL]

CVE: CVE-2026-89669
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: nfsd: initialize copy-notify stateid before publishing it
Commit: e08a3dcaca0505f861e344a387f37f94d95dbdc2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e08a3dcaca0505f861e344a387f37f94d95dbdc2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89669
Analysis date: Fri, 11 Sep 2026 21:32:42 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
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-2026-89669 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89669

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: IMPORTANT
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-2026-89669	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89669 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:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-367;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free can occur in the NFS server COPY_NOTIFY path because the copy notify state object was published before cp_p_stateid and cp_p_clid were fully initialized and before the caller held its own reference. A racing OFFLOAD_CANCEL can reach the published state and free it while nfsd4_copy_notify still reads the returned stateid and writes parent state fields. For the CVSS the PR:L is used because reliable triggering normally requires access as an NFS client that can issue the relevant NFSv4.2 operations and interact with server side copy notify state. The issue is network reachable when the NFS server is exposed to that client, but practical exposure is usually limited to trusted storage or data center networks rather than the public Internet. Impact is at least remote denial of service via kernel crash. Because the race creates a UAF with subsequent reads and writes to the freed object, worst case impact may include confidentiality and integrity compromise and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	OOB DANGER DISK INIT UAF NETWORK LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6. No floor or cap applied.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap applied.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation. The copy-notify state is published into the IDR and parent list before full initialization and before the caller owns a reference. A racing OFFLOAD_CANCEL can free it while nfsd4_copy_notify still uses the same cps pointer.
* +2 Remote reachable / network-triggerable. The vulnerable path is in nfsd and can be reached by NFSv4.2 protocol operations from a client that can interact with the exported NFS service.
* +1 Reliable kernel crash / strong DoS. The stale object is read and then written after it may have been freed, which supports kernel crash or memory corruption.
* +1 Attacker-influenced repeatable lifetime manipulation. The same client-side actor can plausibly drive COPY_NOTIFY creation and racing OFFLOAD_CANCEL attempts repeatedly against server-side copy-notify state.
* +1 Structured stale-object exploitation leverage. The stale object is an active structured nfsd state object, and the stale path performs meaningful reads and writes to stateid/clientid fields after possible free, not merely a shallow cleanup dereference.

Negative signals:

* -1 Conservative hard race / timing window. The UAF depends on a racing OFFLOAD_CANCEL landing after publication and before the caller finishes using the object. This is a real timing requirement, so the lower score applies one conservative penalty.

Paranoid difference:

* The paranoid score withholds the timing penalty because the object identifier is described as guessable and repeated network attempts can plausibly make the race operationally reachable. This does not assume arbitrary code execution.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* CLASS_A is not assigned because the post-free writes are concrete but not shown to be attacker-directed into a chosen replacement object.
* Confidentiality and integrity are not scored as independently demonstrated consequences. They remain worst-case concerns due to UAF with post-free writes.
* Weak LPE is not separately awarded because the relevant exploitation concern is already captured as structured stale-object leverage.
* Extra Availability is not awarded because the same crash/DoS is already counted once.
* Concrete repeated release/refcount signal is not awarded as a primary signal. OFFLOAD_CANCEL can free the object, and the same cps pointer survives in the caller, but the clearly demonstrated stale operations are reads and writes to fields. A second lifetime/refcount mutation is not the main established primitive from the supplied control flow.
* FLOOR 5 is not needed because arithmetic already exceeds 5.

Repeated release/refcount checklist:

* First release can end lifetime: yes, OFFLOAD_CANCEL can free the published copy-notify state.
* Exact same reference survives: yes, the caller keeps cps without owning a reference in the vulnerable version.
* Second operation is a real lifetime/refcount mutation: not clearly established as the primary vulnerable operation. The established operations are stale read and stale writes.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage awarded: no.
* FLOOR 5 applied: no, not needed.

3. Reachability analysis

The evaluated attacker is a remote or adjacent NFS client that can issue relevant NFSv4.2 operations to the vulnerable nfsd service. Host administrator privilege on the victim is not established as required. The attacker does need protocol-level reachability and enough NFS client access to exercise COPY_NOTIFY and OFFLOAD_CANCEL behavior, so this is not an unauthenticated Internet service assumption in all deployments.

Namespace-scoped privilege is not relevant here. This is not a local namespace capability path. Prior host setup exists in the normal operational sense that nfsd and suitable exports must be configured, but that is deployment exposure rather than an attacker-controlled prerequisite.

Special hardware is not required. The race is timing-sensitive, but the relevant operations are network protocol operations and can plausibly be retried. Practical exposure is higher on NFS servers that enable or support server-side copy features and expose NFSv4.2 to less trusted clients.

4. Primitive and severity interpretation

The exact primitive is a network-reachable race-induced UAF in NFS server copy-notify state. The object is active structured kernel state, not fixed stale storage. The vulnerable path is not cleanup-only: after publication and possible freeing by OFFLOAD_CANCEL, nfsd4_copy_notify continues to read the generated stateid and write parent stateid/clientid fields through the stale cps pointer.

This is CLASS_B because a real kernel lifetime/corruption primitive exists and exploitation-leverage analysis is required. It is not CLASS_A because controlled reclaim, attacker-directed write target, arbitrary read/write, callback control, or demonstrated LPE is not established by the supplied evidence.

The demonstrated consequence is at least remote denial of service through kernel crash or memory corruption. The speculative consequence is broader confidentiality or integrity compromise if the post-free writes can be turned into useful heap corruption, but that is not proven here. ImportantCandidate is YES because this is a remote/adjacent protocol-triggerable active-object UAF with post-free writes in nfsd state. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate would discard meaningful unresolved exploitation leverage.

Likely operational severity is Important-candidate for exposed or semi-trusted NFS server deployments, especially where untrusted clients can reach NFSv4.2 server-side copy operations.

5. One-sentence report phrase

A race in the NFS server COPY_NOTIFY path can publish copy-notify state before it is fully initialized and referenced by the caller, allowing a racing OFFLOAD_CANCEL from an NFS client to free the state while nfsd4_copy_notify still reads and writes it, resulting in a network-reachable UAF and at least kernel crash DoS with unresolved memory-corruption impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable active-object UAF with concrete post-free reads and writes in nfsd state, and the difference between crash-only DoS and stronger memory-corruption impact requires human review.

7. Call-site confidence

Call-site confidence: high

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

Patch: nfsd: initialize copy-notify stateid before publishing it
Commit: e08a3dcaca0505f861e344a387f37f94d95dbdc2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e08a3dcaca0505f861e344a387f37f94d95dbdc2

Commit description:

nfsd4_copy_notify() finished initializing the cpntf state after
nfs4_alloc_init_cpntf_state() had already linked it into the
s2s_cp_stateids IDR and the parent's sc_cp_list, with cs_count == 1 (the
membership reference) and none held for the caller. A racing
OFFLOAD_CANCEL (crafted cl_id == nn->s2s_cp_cl_id plus the guessable
so_id) could reach manage_cpntf_state() and free the entry, turning the
caller's subsequent cpn_cnr_stateid read and cp_p_stateid/cp_p_clid
writes into use-after-free. The owning clientid was also only recorded
after publication, so it could not gate an ownership check in that window.

Record cp_p_stateid and cp_p_clid inside nfs4_alloc_init_cpntf_state()
before nfs4_init_cp_state() publishes the entry, and return it with an
extra reference. The caller reads the stateid under that reference and
drops it with nfs4_put_cpntf_state(); on a late error the laundromat
reaps the entry.

Fixes: 624322f ("NFSD add COPY_NOTIFY operation")
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-v3-4-a0ff7db6aa3e@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/nfsd/nfs4proc.c
  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=e08a3dcaca0505f861e344a387f37f94d95dbdc2

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

The original Linux kernel CVE announcement for CVE-2026-89669 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89669

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).