[CVE-2026-64137][IMPORTANT] smb: client: require net admin for CIFS SWN netlink [ Upstream

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

CVE: CVE-2026-64137
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: smb: client: require net admin for CIFS SWN netlink [ Upstream
Commit: 9cf7eb8919344932f909b2fac76296f7656fda8d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cf7eb8919344932f909b2fac76296f7656fda8d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64137
Analysis date: Sun, 19 Jul 2026 11:59:48 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An unprivileged local process could access the CIFS SWN generic netlink interface to receive sensitive SMB witness registration data including NTLM credentials and inject spoofed witness notifications, causing credential disclosure and possible SMB client state disruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64137 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64137

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
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CVE-2026-64137	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-862;*CWE-200;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L';BEST CVSS score: '7.8';DESCR 'The CIFS SWN generic netlink interface allowed any local process to send witness notify commands and to subscribe to the SWN multicast group without CAP_NET_ADMIN. This can expose witness registration data and, for NTLM authenticated mounts, SMB username, domain, and password attributes copied from the CIFS session. A local attacker can also inject RESOURCE_CHANGE or CLIENT_MOVE notifications into the in kernel witness handler, which may disrupt SMB client failover behavior or connection state. For the CVSS the PR:L because a local unprivileged process is sufficient to reach the netlink interface, while full administrator privileges are not required. The issue is not directly network reachable and is triggered through a local generic netlink control interface. Impact includes high confidentiality risk from credential disclosure and possible integrity or availability impact for affected SMB client sessions.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-64137 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DISK SIMPLEFIX SERVERTOCLIENT KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  Any local process could send `CIFS_GENL_CMD_SWN_NOTIFY` and join `CIFS_GENL_MCGRP_SWN` before the fix.

* Security-boundary bypass with practical sensitive-object access: +2
  The missing `CAP_NET_ADMIN` checks bypass an intended generic-netlink capability boundary.

* Sensitive credential theft primitive: +2
  Multicast registration messages may include witness registration id and, for NTLM-authenticated mounts, SMB username, domain, and password attributes copied from the CIFS session.

* Confidentiality impact plausible: +1
  Credential exposure is explicitly described and is the strongest confirmed impact.

* Integrity impact plausible: +1
  Unprivileged local processes could inject `RESOURCE_CHANGE` or `CLIENT_MOVE` witness notifications into the in-kernel handler.

* Availability impact realistic: +1 in paranoid score
  Spoofed witness notifications may disrupt SMB client failover behavior or connection state. This is plausible but more environment-dependent, so it is counted in the higher score.

* Rare or configuration-dependent exposure: -1 in conservative score
  Practical credential exposure depends on CIFS/SMB client usage, SWN witness functionality, and NTLM-authenticated mounts.

No memory corruption, UAF, OOB write, or arbitrary code execution primitive is indicated by the patch.

## 3. Reachability analysis

The bug is locally reachable through the CIFS generic-netlink interface. A local unprivileged process can trigger it before the patch, so this is not PR:H in practical terms. It is not directly network-triggerable by a remote host. Namespaces matter because the fix uses `GENL_MCAST_CAP_NET_ADMIN`, requiring `CAP_NET_ADMIN` over the relevant network namespace for multicast group access. The affected path is only relevant when CIFS/SMB client witness support is present and active, but the exposed netlink permission mistake is direct and does not require memory-corruption exploitation.

## 4. Severity interpretation

This behaves more like an Important-class access-control and credential-disclosure bug than an ordinary Moderate DoS. The realistic confirmed impact is local disclosure of SMB authentication material from kernel-generated witness registration messages. The notification spoofing path adds plausible integrity and availability impact for SMB client session handling, but without evidence of memory corruption or privilege escalation to kernel code execution.

## 5. One-sentence report phrase

An unprivileged local process could access the CIFS SWN generic netlink interface to receive sensitive SMB witness registration data including NTLM credentials and inject spoofed witness notifications, causing credential disclosure and possible SMB client state disruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Confirmed local credential disclosure is present, and the affected data may include SMB username, domain, and password attributes. This should not be auto-closed even though the bug is not memory corruption and is not directly network reachable.

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

Patch: smb: client: require net admin for CIFS SWN netlink [ Upstream
Commit: 9cf7eb8919344932f909b2fac76296f7656fda8d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cf7eb8919344932f909b2fac76296f7656fda8d

Changed files:
  fs/cifs/netlink.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=9cf7eb8919344932f909b2fac76296f7656fda8d

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

The original Linux kernel CVE announcement for CVE-2026-64137 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64137

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:L/UI:N/S:U/C:H/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 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).