[CVE-2026-90235][MODERATE 7.0] sunrpc: xprtsock: annotate shared socket callbacks with READ_ONCE/WRITE_ONCE [ Upstream

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

CVE: CVE-2026-90235
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: sunrpc: xprtsock: annotate shared socket callbacks with READ_ONCE/WRITE_ONCE [ Upstream
Commit: ed80d009b154aa204f541d390884851b3d4f15ae
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed80d009b154aa204f541d390884851b3d4f15ae
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90235
Analysis date: Fri, 18 Sep 2026 06:54:11 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90235 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90235

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.

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

CVE-2026-90235	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90235 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:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-662;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'SUNRPC xprtsock updates shared socket callback pointers for sk_data_ready and sk_write_space on live AF_LOCAL UDP and TCP sockets without READ_ONCE() and WRITE_ONCE() visibility annotations. Generic socket and protocol paths may read or invoke these callbacks concurrently, so a stale callback snapshot can call xs_data_ready() or xs_udp_write_space() after the socket has been restored to lower level handlers during teardown. This is a race condition and UAF candidate because the stale callback may operate on SUNRPC transport state after ownership is changing or gone, causing at least kernel crash or service disruption. For the CVSS the PR:N is selected because a malicious RPC peer or MITM does not need local privileges on the victim once the client uses the affected SUNRPC transport. The issue is network reachable in NFS or SUNRPC client deployments, but practical exploitation usually requires timing the connection teardown or reconnect path and access as the contacted server or network path. Impact is at least denial of service and the paranoid score treats memory safety impact as possible, so manual review is needed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	YES	REMOTE DANGER NETWORK HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

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. The paranoid score is emitted as the final ActionableScore because the issue is network influenced, affects live socket callback dispatch, and has unresolved teardown timing behavior.

2. Signal breakdown

Conservative positive signals:

* +2 Remote reachable / network influenced: a malicious or compromised SUNRPC/NFS peer or MITM can plausibly influence socket events once the victim client is using the affected SUNRPC transport.
* +1 Weak / indirect active callback state primitive: shared live socket callback pointers are replaced and restored without READ_ONCE/WRITE_ONCE, allowing stale callback snapshots to invoke SUNRPC callbacks after the socket callback fields have been restored.
* +1 Strong DoS concern: stale callback execution in the wrong transport state can plausibly cause kernel crash or service disruption, even though a full exploit primitive is not demonstrated.

Paranoid additional signal:

* +1 Broad deployed exposure: SUNRPC/NFS client transports over TCP, UDP, and AF_LOCAL are not obscure kernel-only test paths and are realistically exercised in storage and enterprise deployments.

Negative signals:

* No -1 race penalty was applied. The issue is a race, but the supplied evidence does not prove that the timing is one-shot, externally uncontrollable, or impractical to repeat.
* No -2 host-admin penalty was applied. The evaluated attacker is a remote peer or MITM against an already configured SUNRPC/NFS client transport, not a local host administrator.
* No rare subsystem penalty was applied. SUNRPC/NFS is specialized by deployment but not rare in relevant environments.

Important non-awarded signals:

* RealUAF was not awarded because the patch establishes stale callback invocation after callback restoration, but does not directly prove access to freed transport storage.
* Controlled reclaim is not demonstrated.
* Arbitrary write is not demonstrated.
* Confidentiality and integrity impact are not awarded because no disclosure, directed write, credential corruption, or security-boundary bypass is established.
* Strong LPE leverage is not awarded. The callback pointer values are legitimate kernel callbacks, not attacker-controlled function pointers.
* Extra availability was not awarded because the same crash or service disruption is already counted once.
* Concrete repeated release/refcount was not awarded. The patch does not show a first put/free followed by a second lifetime-mutating operation on the exact same dangling reference.
* Structured stale-object leverage was not separately awarded because a real post-free structured-object consumption path is not directly established.

Repeated release/refcount checklist:

* First release can end lifetime: not established.
* Exact same reference survives: not established.
* Second operation mutates lifetime/refcount: not established.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.

3. Reachability analysis

The most plausible attacker is a malicious SUNRPC/NFS server or a MITM on the network path to an already configured client. Such an attacker does not need local code execution or host-admin privilege on the victim, but practical triggering likely depends on connection teardown, reconnect, or socket event timing.

This is not a namespace-scoped privilege case. No CAP_NET_ADMIN or namespace capability chain is needed for the remote-peer model, and no complete namespace-local trigger is shown.

There may be prior privileged setup in real deployments because NFS mounts or SUNRPC client configuration are often established by an administrator. That does not make the remote peer host-admin once the client is already using the transport.

No special hardware or firmware prerequisite is visible. The affected paths cover AF_LOCAL, UDP, and TCP SUNRPC transports. Race repeatability is uncertain but not proven to be hard enough to subtract a timing penalty.

4. Primitive and severity interpretation

The exact primitive is a shared live socket callback visibility race. xprtsock replaces and restores sk_data_ready and sk_write_space while generic socket or protocol code may concurrently read or invoke those callbacks. A stale callback snapshot may invoke xs_data_ready or xs_udp_write_space after the socket callback fields have already been restored to the lower-socket handlers.

This is an active callback state and teardown synchronization issue, not a proven arbitrary function-pointer overwrite. It is also not a directly established UAF from the supplied patch alone, because the evidence does not show that the SUNRPC transport object is freed before the stale callback consumes it.

PrimitiveClass is CLASS_B because callback dispatch on live kernel socket state is security-sensitive and the stale callback behavior leaves unresolved memory/lifetime consequences beyond a simple validation bug. RealUAF remains NO because post-lifetime use is only a candidate, not directly established.

Demonstrated consequence is invalid stale callback invocation and likely DoS or service disruption. Speculative consequence is a stronger UAF or memory-safety issue if stale SUNRPC callback execution races with transport teardown and freed state, but controlled reclaim or useful corruption is not shown.

ImportantCandidate is NO because no Class A primitive, concrete UAF, controlled reclaim, directed write, security-boundary bypass, or demonstrated LPE is established. AutoDowngradeAllowed is NO because the issue is network influenced and affects live kernel callback dispatch, so automatic closure as an ordinary low-risk issue would be unsafe without manual review.

Likely operational severity is Actionable Moderate.

5. One-sentence report phrase

A SUNRPC xprtsock callback visibility race can let a stale socket callback snapshot invoke SUNRPC handlers after callback restoration during teardown, allowing a malicious RPC peer or MITM to potentially cause kernel service disruption or crash in affected NFS/SUNRPC client deployments.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is network influenced and involves live socket callback dispatch during teardown, with unresolved lifetime implications even though a concrete UAF or exploitation primitive is not proven from the patch alone.

7. Call-site confidence

Call-site confidence: high

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

Patch: sunrpc: xprtsock: annotate shared socket callbacks with READ_ONCE/WRITE_ONCE [ Upstream
Commit: ed80d009b154aa204f541d390884851b3d4f15ae
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed80d009b154aa204f541d390884851b3d4f15ae

Changed files:
  net/sunrpc/xprtsock.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=ed80d009b154aa204f541d390884851b3d4f15ae

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

The original Linux kernel CVE announcement for CVE-2026-90235 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90235

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: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:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 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).