[CVE-2026-52925][MODERATE REGULAR] vrf: Fix a potential NPD when removing a port from a VRF [ Upstream

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

CVE: CVE-2026-52925
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vrf: Fix a potential NPD when removing a port from a VRF [ Upstream
Commit: 2c022f582fd16a470df6ed9e7fb7e9fc48946d49
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2c022f582fd16a470df6ed9e7fb7e9fc48946d49
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52925
Analysis date: Wed, 24 Jun 2026 04:06:34 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A VRF port removal RCU race can let local network configuration changes cause an RCU reader to dereference missing l3mdev operations, leading to a kernel NULL pointer dereference and local DoS, with higher concern in delegated CAP_NET_ADMIN namespace environments.

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

The original Linux kernel CVE announcement for CVE-2026-52925 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52925

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 REGULAR
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-2026-52925	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-362;**CWE-476;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in VRF port removal can let an RCU reader observe a device as an l3mdev slave and then obtain a non VRF master device such as a bridge. The reader may then dereference missing l3mdev operations in l3mdev_fib_table_rcu() and crash the kernel. For the CVSS the PR:L is used for the paranoid score because triggering the race typically requires local control over VRF or netdevice configuration through CAP_NET_ADMIN or an equivalent delegated network administration context. The issue is not directly network reachable through packet traffic and is triggered through local network control plane changes. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to the RCU race context and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)	YES	DANGER NULLPTR NETWORK HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Paranoid score signals:

* RCU lifetime / synchronization issue: +1
  The patch adds `synchronize_net()` after clearing `IFF_L3MDEV_SLAVE`, showing an RCU reader consistency window.
* Reliable kernel crash / strong DoS: +1
  The commit provides a concrete NULL pointer dereference in `l3mdev_fib_table_rcu()`.
* Local unprivileged or delegated namespace concern: +1
  In some deployments, unprivileged users may obtain `CAP_NET_ADMIN` inside a user or network namespace and manipulate VRF devices if allowed.
* Hard or unreliable race / special timing required: -1
  Triggering requires racing VRF slave removal or reconfiguration with an RCU reader path such as `bind()`.
* Typical `CAP_NET_ADMIN` requirement: conservative penalty applies
  In normal host deployments, removing a port from a VRF requires `CAP_NET_ADMIN`, lowering the conservative score.

Not counted:

* No remote/network-triggerable packet path: +0
  This is a local network control-plane race, not a packet parsing bug.
* No generic strong memory corruption: +0
  The demonstrated failure is NULL pointer dereference, not UAF, OOB write, type confusion, or attacker-controlled reuse.
* No privilege escalation plausible signal: +0
  The patch does not show a reclaim primitive, callback dispatch, writable stale object, refcount takeover, or arbitrary write.
* No confidentiality or integrity impact in the conservative score: +0
  The evidence supports DoS, not data disclosure or modification.

## 3. Reachability analysis

The bug is triggered by removing or reconfiguring a port from a VRF while an RCU reader still treats the device as an L3 master device slave. The observed crash path can involve an ordinary syscall such as `bind()`, but the attacker normally needs control over VRF or netdevice configuration to create the race window.

In typical host deployments this requires `CAP_NET_ADMIN`, so the conservative score is low. In containerized or namespace-enabled environments, `CAP_NET_ADMIN` may be delegated to less trusted users, which makes the paranoid score higher. The affected path is not remotely reachable through packet traffic. VRF is not universally enabled by default, but it is a standard Linux networking feature used in routing and multi-tenant network setups.

## 4. Severity interpretation

This behaves more like an ordinary Moderate or borderline actionable Moderate issue, not an Important-class vulnerability. The realistic demonstrated impact is local DoS through a kernel NULL pointer dereference. The theoretical concern comes from the RCU synchronization bug class, but the patch and commit do not show UAF reclaim, stale object reuse, writable memory corruption, type confusion, or a privilege escalation primitive.

Because the bug is an RCU race in networking code and namespace delegation can reduce the practical privilege requirement, it should not be blindly auto-closed without at least lightweight manual review.

## 5. One-sentence report phrase

A VRF port removal RCU race can let local network configuration changes cause an RCU reader to dereference missing l3mdev operations, leading to a kernel NULL pointer dereference and local DoS, with higher concern in delegated CAP_NET_ADMIN namespace environments.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is an RCU synchronization bug in networking with a concrete kernel crash and possible namespace-dependent reachability. It is not a strong Important candidate because the demonstrated primitive is NULL pointer dereference only, without supported evidence of UAF reuse, arbitrary write, information disclosure, or privilege escalation.

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

Patch: vrf: Fix a potential NPD when removing a port from a VRF [ Upstream
Commit: 2c022f582fd16a470df6ed9e7fb7e9fc48946d49
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2c022f582fd16a470df6ed9e7fb7e9fc48946d49

Changed files:
  net/l3mdev/l3mdev.c
  net/ipv4/af_inet.c
  include/linux/file.h
  net/socket.c
  arch/x86/entry/syscall_64.c
  arch/x86/entry/entry_64.S
  drivers/net/vrf.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=2c022f582fd16a470df6ed9e7fb7e9fc48946d49

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

The original Linux kernel CVE announcement for CVE-2026-52925 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52925

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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 1
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).