[CVE-2026-68142][IMPORTANT] geneve: require CAP_NET_ADMIN in the device netns for changelink

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

CVE: CVE-2026-68142
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: geneve: require CAP_NET_ADMIN in the device netns for changelink
Commit: 2abdacc927c92fa6a9cc8341e8c9b88dcb561553
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2abdacc927c92fa6a9cc8341e8c9b88dcb561553
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68142
Analysis date: Mon, 10 Aug 2026 20:20:39 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Geneve changelink lacked a CAP_NET_ADMIN check against the sticky underlay network namespace, allowing a caller authorized only in the device namespace to reconfigure Geneve underlay state in another namespace, potentially causing tunnel policy bypass, traffic redirection, or disruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68142 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68142

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-2026-68142	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H';CWE-862;CWE-269;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:L';BEST CVSS score: '8.8';DESCR 'Geneve changelink missed an authorization check against the sticky underlay network namespace. A process with CAP_NET_ADMIN only in dev_net(dev) could change a Geneve device whose underlay sockets live in geneve net, causing configuration changes in a namespace where it is not authorized. For the CVSS the PR:L is used because the attacker needs local capability in one network namespace, but not administrative rights in the affected underlay namespace. The issue is not directly network reachable because it is triggered through rtnetlink control plane operations. Impact is a cross namespace access control bypass with possible tunnel traffic redirection, policy bypass, or disruption of Geneve underlay sockets.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	NETWORK HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	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

Triggered signals:

* Security-boundary bypass with practical sensitive-object access: +2
  The bug bypasses the intended CAP_NET_ADMIN check for the sticky Geneve underlay netns. A caller authorized only in dev_net(dev) can affect configuration and sockets in geneve->net.

* Cross-boundary isolation/policy bypass: +1
  The affected condition appears specifically when device netns and underlay netns differ, which is a namespace isolation boundary issue.

* Practical exploit chain strongly implied: +1
  The commit directly states that a caller privileged in one netns but not in geneve->net can rewrite the Geneve device and cause underlay socket reopen/configuration in the unauthorized namespace.

* Confidentiality impact plausible: +1
  Tunnel reconfiguration can plausibly affect where encapsulated traffic flows, creating possible traffic exposure depending on deployment.

* Integrity impact plausible: +1
  Unauthorized Geneve configuration changes can redirect, alter, or policy-bypass tunnel behavior.

* Availability impact realistic: +1
  Unauthorized quiesce/unquiesce and underlay socket changes can disrupt Geneve tunnel connectivity.

Subtract / constraints:

* Requires CAP_NET_ADMIN in at least one namespace: -1
  This is not fully unprivileged, but the full -2 admin penalty should not apply because the vulnerability is precisely a capability or namespace boundary bypass. Container root or delegated CAP_NET_ADMIN in one netns is not equivalent to CAP_NET_ADMIN in the affected underlay netns.

No memory-corruption signals are applied. This is an authorization and namespace isolation bug, not UAF/OOB/type confusion.

## 3. Reachability analysis

The bug is triggered locally through rtnetlink changelink operations on a Geneve device. It is not directly network-triggerable by packet traffic.

The realistic attacker is a local process, container root, or service with CAP_NET_ADMIN in the device namespace but without CAP_NET_ADMIN in the sticky underlay namespace geneve->net. Namespace delegation matters heavily here because the vulnerability allows influence across a boundary that should have required separate authorization.

The path requires Geneve devices and a configuration where dev_net(dev) differs from geneve->net, for example after device creation or movement across namespaces. This is not a public Internet remote attack, but it is relevant in containerized, virtualized, or multi-tenant networking environments using Geneve overlays.

## 4. Severity interpretation

This behaves more like an Important-class authorization bypass than an ordinary Moderate correctness issue. There is no demonstrated memory corruption or kernel crash primitive, so memory-corruption scoring should not be applied.

The security impact comes from crossing a namespace and capability boundary. In conservative handling, this is an Actionable Moderate because it can change tunnel state outside the attacker's authorized namespace. In the paranoid interpretation, it is a Strong Important candidate because unauthorized Geneve underlay reconfiguration can plausibly affect confidentiality, integrity, and availability of overlay traffic in container or cloud networking deployments.

## 5. One-sentence report phrase

Geneve changelink lacked a CAP_NET_ADMIN check against the sticky underlay network namespace, allowing a caller authorized only in the device namespace to reconfigure Geneve underlay state in another namespace, potentially causing tunnel policy bypass, traffic redirection, or disruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because it is a cross-namespace capability bypass with practical impact on tunnel configuration and underlay sockets. Even without memory corruption, the affected boundary is security-relevant in container and multi-tenant networking deployments.

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UPSTREAM PATCH SUMMARY
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Patch: geneve: require CAP_NET_ADMIN in the device netns for changelink
Commit: 2abdacc927c92fa6a9cc8341e8c9b88dcb561553
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2abdacc927c92fa6a9cc8341e8c9b88dcb561553

Commit description:

A tunnel changelink() operates on at most two netns, dev_net(dev) and
the sticky underlay netns geneve->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 geneve->net can rewrite a geneve
device whose underlay lives in geneve->net.

geneve_changelink() applies the new configuration against geneve->net:
geneve_link_config() and the geneve_quiesce()/geneve_unquiesce() pair
reopen the underlay sockets in that netns (geneve_sock_add() uses
geneve->net), so the same reasoning as the tunnel changelink series
applies here.

Gate geneve_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: 5b861f6 ("geneve: add rtnl 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/20260716203500.70573-3-doruk@0sec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/geneve.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=2abdacc927c92fa6a9cc8341e8c9b88dcb561553

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

The original Linux kernel CVE announcement for CVE-2026-68142 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68142

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:C/C:L/I:H/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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).