[CVE-2026-68432][IMPORTANT] vxlan: require CAP_NET_ADMIN in the device netns for changelink

[CVE-2026-68432][IMPORTANT] vxlan: require CAP_NET_ADMIN in the device netns for changelink

[AL-KERNEL]

CVE: CVE-2026-68432
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: vxlan: require CAP_NET_ADMIN in the device netns for changelink
Commit: b3793d7dccb192ffff29894d11824db6251acdd5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3793d7dccb192ffff29894d11824db6251acdd5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68432
Analysis date: Tue, 11 Aug 2026 20:57:45 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A VXLAN changelink authorization bypass allows a caller with CAP_NET_ADMIN only in the device netns to modify configuration applied in the sticky underlay netns, potentially affecting tunneled traffic confidentiality, integrity, and availability.

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

The original Linux kernel CVE announcement for CVE-2026-68432 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68432

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-2026-68432	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H';CWE-862;CWE-269;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:L';BEST CVSS score: '7.8';DESCR 'A VXLAN changelink authorization bypass can occur when the VXLAN device netns differs from the sticky underlay netns used by vxlan net. The rtnl changelink path checks CAP_NET_ADMIN only in dev_net(dev), while vxlan_changelink validates and applies the new configuration against the underlay netns and may reopen the underlay socket there. For the CVSS the PR:L is used because the practical attacker needs local code execution with CAP_NET_ADMIN only in the device netns, such as container root or a delegated network administration context, but lacks CAP_NET_ADMIN in the sticky underlay netns. The issue is not directly network reachable and is triggered through local netlink/rtnl control plane operations. Impact is a cross namespace network administration bypass that can alter VXLAN tunnel configuration and may affect confidentiality, integrity, and availability of tunneled traffic depending on deployment.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	SIMPLEFIX NETWORK HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Security-boundary bypass with practical sensitive-object access: +2
  The bug bypasses the intended CAP_NET_ADMIN boundary between dev_net(dev) and the sticky VXLAN underlay netns.
* Cross-boundary isolation/policy bypass: +1
  A caller privileged only in the device netns can affect configuration applied in another netns.
* Integrity impact plausible: +1
  The attacker can rewrite VXLAN tunnel configuration and potentially redirect or alter overlay traffic behavior.
* Availability impact realistic: +1
  Incorrect VXLAN reconfiguration can break tunnel connectivity or disrupt underlay socket behavior.
* Special namespace setup required: -1
  The issue requires dev_net(dev) and vxlan->net to differ, such as after device creation or movement across namespaces.

Paranoid additional signals:

* Confidentiality impact plausible: +1
  VXLAN reconfiguration may expose or redirect tunneled traffic depending on deployment.
* Practical exploit chain strongly implied: +1
  The commit explicitly states that vxlan_changelink() validates and applies configuration against vxlan->net and can reopen the underlay socket there.

No memory corruption signal is applied. No remote-network trigger signal is applied. This is an authorization and namespace capability bypass, not a packet-processing bug.

## 3. Reachability analysis

The trigger is local netlink/rtnl control-plane access to changelink for a VXLAN device. The attacker does not need full host root, but does need CAP_NET_ADMIN in the device netns while lacking CAP_NET_ADMIN in the sticky underlay netns. This is relevant for container root, delegated network administration, or namespace-separated service accounts.

The path is not directly reachable by incoming network packets. It depends on VXLAN being configured and on a namespace arrangement where the device namespace differs from vxlan->net. VXLAN is common in container, virtualization, and overlay networking environments, so the exposure is realistic even though it is not a default remote attack surface.

## 4. Severity interpretation

This behaves more like an Important-class authorization bypass than an ordinary Moderate bug. There is no evidence of UAF, OOB write, type confusion, or arbitrary kernel memory corruption. The practical risk comes from crossing a namespace capability boundary and allowing a reduced-privilege network administrator to modify VXLAN state tied to another netns.

The conservative score is Actionable Moderate because exploitation needs a specific namespace and capability setup. The paranoid score reaches Strong Important candidate because the bypass can affect confidentiality, integrity, and availability of tunneled traffic in real VXLAN deployments.

## 5. One-sentence report phrase

A VXLAN changelink authorization bypass allows a caller with CAP_NET_ADMIN only in the device netns to modify configuration applied in the sticky underlay netns, potentially affecting tunneled traffic confidentiality, integrity, and availability.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a cross-namespace capability bypass with plausible container or delegated-admin impact, even though it is not memory corruption and is not directly network-triggerable.

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

Patch: vxlan: require CAP_NET_ADMIN in the device netns for changelink
Commit: b3793d7dccb192ffff29894d11824db6251acdd5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3793d7dccb192ffff29894d11824db6251acdd5

Commit description:

A tunnel changelink() operates on at most two netns, dev_net(dev) and
the sticky underlay netns vxlan->net. They differ once the device is
created in or moved to a netns other than the one the request runs in.
The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev),
so a caller privileged there but not in vxlan->net can rewrite a vxlan
device whose underlay lives in vxlan->net.

vxlan_changelink() validates and applies the new configuration against
vxlan->net (vxlan_config_validate(vxlan->net, ...)) and can reopen the
underlay socket in that netns, so the same reasoning as the tunnel
changelink series applies here.

Gate vxlan_changelink() with rtnl_dev_link_net_capable(), at the top of
the op before any attribute is parsed, matching ipgre_changelink() and
the rest of the "require CAP_NET_ADMIN in the device netns for
changelink" series.

Found by 0sec automated security-research tooling ( https://0sec.ai ).

Fixes: 8bcdc4f ("vxlan: add changelink support")
Cc: stable@vger.kernel.org
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Link: https://patch.msgid.link/20260716203500.70573-2-doruk@0sec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/vxlan/vxlan_core.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=b3793d7dccb192ffff29894d11824db6251acdd5

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

The original Linux kernel CVE announcement for CVE-2026-68432 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68432

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:C/C:L/I:H/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/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: 5
  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).