[CVE-2026-90102][MODERATE 7.0] NFSv4/pnfs: key the data server cache on the NFS version [ Upstream

[CVE-2026-90102][MODERATE 7.0] NFSv4/pnfs: key the data server cache on the NFS version [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90102
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: NFSv4/pnfs: key the data server cache on the NFS version [ Upstream
Commit: ffb100b0da0e217d5d63ce6fe092f9c29e59f7dd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ffb100b0da0e217d5d63ce6fe092f9c29e59f7dd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90102
Analysis date: Fri, 18 Sep 2026 04:36:33 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90102 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90102

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-90102	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90102 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-697;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A NULL pointer dereference can occur in the NFSv4 pNFS flexfiles path because the per net data server cache was keyed only by the multipath address set and did not include the NFS major version. A server can return two deviceids for the same address with different NFS versions, causing NFSv3 and NFSv4 data server entries to alias and reuse a client with mismatched rpc_call_ops and rpc_ops. The mismatch can break sequence slot handling and crash the kernel on the NFS client. For the CVSS the PR:N is used because a malicious or compromised NFS server does not need a local account on the client once the client is connected. The issue is network influenced, but practical exposure usually requires pNFS flexfiles and access to a trusted storage or data center network rather than the public Internet. Impact is denial of service via kernel crash. No direct confidentiality or integrity impact is indicated because the patch shows a NULL pointer dereference rather than a UAF, OOB write, or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	YES	OOB DISK SIMPLEFIX NETWORK HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate**::

No floor or cap was applied. Paranoid score is higher because the issue is network influenced by server supplied pNFS flexfiles metadata in an important storage client path, but still remains crash or DoS only.

2. Signal breakdown

Conservative positive signals:

* +2 Remote reachable / network influenced. A malicious or compromised NFS server can supply GETDEVICEINFO / pNFS flexfiles metadata that causes NFSv3 and NFSv4 data server cache aliasing on the client.
* +1 Reliable kernel crash / strong DoS. The commit explicitly states that mismatched sequence slot handling dereferences NULL.
* +1 Weak / indirect corruption candidate. The bug is a wrong object selection / semantic mismatch where an nfs4_pnfs_ds object is reused for an incompatible NFS major version, leading to invalid rpc_call_ops / rpc_ops use.

Paranoid additional signal:

* +1 Important storage client path. The bug is in NFS pNFS flexfiles data server selection and is driven by server supplied storage topology metadata. This raises practical triage priority but does not establish memory corruption.

Non-awarded signals:

* RealUAF not awarded. The patch indicates NULL dereference from wrong client version reuse, not use after free.
* Controlled reclaim not demonstrated.
* Arbitrary or directed write not demonstrated.
* Confidentiality and integrity not awarded. The evidence supports crash only, not information disclosure or unauthorized modification.
* Strong semantic reinterpretation not awarded. The NFS major version mismatch is security relevant for crash reachability, but the supplied evidence does not show attacker controlled active operations beyond causing invalid NULL dereference.
* Extra availability not awarded. The same kernel crash is already counted once.
* ImportantCandidate not set. No Class A primitive, no real UAF, and no unresolved strong Class B exploitation primitive is established.

Negative signals:

* No host admin penalty. The attacker model is a malicious or compromised NFS server influencing an already connected client, not a local host administrator.
* No rare subsystem penalty. pNFS flexfiles is deployment specific, but the prompt requires concrete evidence before subtracting for niche exposure.

3. Reachability analysis

The practical attacker is a malicious or compromised NFS server, or an attacker able to influence the pNFS flexfiles server metadata returned to the client. The client must be using NFSv4 pNFS flexfiles and must receive two deviceids for one address with different NFS major versions.

No local account on the client is required for that server side attacker once the client is connected. HostAdminRequired is NO for the attacker who controls the server response. There may be prior legitimate administrative setup to mount or use the NFS export, but that is not the attacker privilege needed to trigger the vulnerable client side path after the storage relationship exists.

NamespaceScopedPrivilege is NO because namespaces are not material to this bug.

The issue is not public Internet typical. NFS and pNFS are normally used on trusted storage or data center networks. Exposure is therefore usually limited to environments where a client connects to an untrusted, compromised, or attacker influenced NFS server.

No race is required. The trigger is a protocol and cache key logic condition.

4. Primitive and severity interpretation

The exact primitive is an invalid state / wrong object selection bug in the pNFS data server cache. The cache key used only the multipath address set and omitted the NFS major version. For flexfiles, two deviceids can legitimately reference the same address with different versions. This can cause an NFSv3 data server and an NFSv4 data server to alias to one shared nfs4_pnfs_ds object.

The stale or wrong object is active structured state, but the demonstrated terminal behavior is a NULL pointer dereference caused by mismatched rpc_call_ops / rpc_ops and sequence slot handling. This is not a UAF, not a double release, and not a concrete refcount lifetime mutation.

PrimitiveClass is CLASS_C because the demonstrated behavior is crash / DoS through invalid state and NULL dereference. It is not CLASS_B because no real lifetime violation is established. It is not CLASS_A because there is no controlled corruption, authorization bypass, COW violation, arbitrary write, or demonstrated privilege escalation.

Demonstrated consequence: kernel crash / denial of service on the NFS client.

Speculative consequence: stronger impact would require an additional primitive such as controlled memory corruption, disclosure, or privileged state modification, none of which is supported by this patch.

ImportantCandidate is NO because the patch supports DoS only. AutoDowngradeAllowed is YES because no meaningful unresolved corruption or boundary primitive remains, although manual review is still recommended due to network influenced kernel crash in a storage client path.

Likely operational severity: actionable Moderate, especially for environments using pNFS flexfiles with less trusted storage servers.

5. One-sentence report phrase

A malicious or compromised NFS pNFS flexfiles server can cause NFSv3 and NFSv4 data server cache aliasing on the client, leading to mismatched RPC operation handling and a NULL pointer dereference that crashes the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is network influenced and can crash the kernel client, but the supplied patch supports NULL dereference DoS only and does not establish UAF, arbitrary write, information disclosure, authorization bypass, or privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: NFSv4/pnfs: key the data server cache on the NFS version [ Upstream
Commit: ffb100b0da0e217d5d63ce6fe092f9c29e59f7dd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ffb100b0da0e217d5d63ce6fe092f9c29e59f7dd

Changed files:
  fs/nfs/filelayout/filelayoutdev.c
  fs/nfs/flexfilelayout/flexfilelayoutdev.c
  fs/nfs/pnfs.h
  fs/nfs/pnfs_nfs.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=ffb100b0da0e217d5d63ce6fe092f9c29e59f7dd

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

The original Linux kernel CVE announcement for CVE-2026-90102 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90102

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