[CVE-2026-72061][IMPORTANT] net: sit: require CAP_NET_ADMIN in the device netns for changelink

[CVE-2026-72061][IMPORTANT] net: sit: require CAP_NET_ADMIN in the device netns for changelink

[AL-KERNEL]

CVE: CVE-2026-72061
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net: sit: require CAP_NET_ADMIN in the device netns for changelink
Commit: cb41b308e9d867725d965b291dd085028e36a480
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cb41b308e9d867725d965b291dd085028e36a480
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72061
Analysis date: Sun, 16 Aug 2026 07:06:17 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing CAP_NET_ADMIN check in ipip6_changelink allowed a caller authorized only in the device netns to rewrite SIT tunnel parameters belonging to a different tunnel link netns, causing a namespace capability bypass with integrity and availability impact.

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

The original Linux kernel CVE announcement for CVE-2026-72061 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72061

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
======================================================================

CVE-2026-72061	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:C/C:L/I:H/A:H';CWE-863;CWE-862;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:H';BEST CVSS score: '8.7';DESCR 'ipip6_changelink can be called for a SIT tunnel whose device namespace and tunnel link namespace are different, but the old rtnl changelink path checked CAP_NET_ADMIN only in dev_net(dev). A caller with CAP_NET_ADMIN in the device namespace but not in the tunnel link namespace could rewrite tunnel parameters that belong to another netns, crossing the intended network namespace privilege boundary. For the CVSS the PR:L is used because the attacker still needs local code execution and delegated network administration capability in one namespace, but not full privilege in the protected tunnel namespace. The issue is not directly network reachable and is triggered through local rtnetlink control plane operations. Impact is mainly integrity and availability of the affected tunnel configuration, with possible limited confidentiality impact if tunnel traffic can be redirected or exposed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE SIMPLEFIX NETWORK HARDWARE IPV6 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 check for the tunnel link netns and allows configuration changes across a namespace privilege boundary.

* Cross-boundary isolation/policy bypass: +1
  The affected object can belong to a different network namespace than the namespace where the caller is authorized.

* Practical exploit chain strongly implied: +1
  The commit directly describes the chain: caller has CAP_NET_ADMIN in dev_net(dev), lacks it in t->net, but can still rewrite the tunnel.

* Integrity impact plausible: +1
  Tunnel parameters can be modified without authorization in the owning tunnel namespace.

* Availability impact realistic: +1
  Rewriting tunnel configuration can disrupt connectivity or break tunnel routing.

* Requires delegated CAP_NET_ADMIN, but not full target privilege: -1
  The attacker is not fully unprivileged, but this is not equivalent to full host root because the flaw bypasses a meaningful namespace capability boundary.

* Cross-netns SIT setup is configuration-dependent: -1
  Triggering requires SIT tunnel use with differing dev_net(dev) and tunnel link netns.

Paranoid adjustment:

* Remove the configuration-dependence penalty: +1 relative to conservative
  If such cross-netns tunnel setups are present in containerized or delegated-network environments, exploitation is straightforward through rtnetlink control-plane operations.

* Confidentiality impact plausible: +1
  Tunnel rewrite may redirect or expose traffic, although there is no kernel memory disclosure primitive.

## 3. Reachability analysis

The bug is locally reachable through rtnetlink changelink operations, not by sending ordinary network packets. The attacker needs CAP_NET_ADMIN in the device namespace, but not in the tunnel link namespace that owns the SIT tunnel state. This matters for containers, delegated network namespaces, sandboxed root, or reduced-capability service accounts, because the bug crosses the intended namespace authorization boundary. It is not a default remote attack surface and requires SIT tunnel configuration with cross-netns behavior.

## 4. Severity interpretation

This is not memory corruption and does not imply arbitrary code execution or direct kernel privilege escalation. Realistic impact is an authorization bypass across network namespaces that can modify another namespace tunnel configuration. That makes it more serious than an ordinary Moderate control-plane bug, because it breaks a capability boundary and may affect traffic integrity, availability, and possibly confidentiality. Conservative handling is Actionable Moderate. Paranoid handling is a Strong Important candidate when cross-netns tunnel delegation is used.

## 5. One-sentence report phrase

A missing CAP_NET_ADMIN check in ipip6_changelink allowed a caller authorized only in the device netns to rewrite SIT tunnel parameters belonging to a different tunnel link netns, causing a namespace capability bypass with integrity and availability impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a cross-netns capability bypass rather than a simple local admin-only configuration bug, and the practical severity depends on container or namespace delegation models in the affected product.

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

Patch: net: sit: require CAP_NET_ADMIN in the device netns for changelink
Commit: cb41b308e9d867725d965b291dd085028e36a480
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cb41b308e9d867725d965b291dd085028e36a480

Commit description:

ipip6_changelink() operates on at most two netns, dev_net(dev) and the
tunnel link netns t->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 t->net can rewrite a tunnel that
lives in t->net.

Gate ipip6_changelink() on rtnl_dev_link_net_capable() at its top,
before any attribute is parsed. sit was the one tunnel type not covered
by the recent series that added this check to the other changelink()
handlers.

Fixes: 5e6700b ("sit: add support of x-netns")
Link: https://lore.kernel.org/netdev/20260612085941.3158249-1-maoyixie.tju@gmail.com/
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260618070817.3378283-1-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/sit.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=cb41b308e9d867725d965b291dd085028e36a480

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

The original Linux kernel CVE announcement for CVE-2026-72061 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72061

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:H
  The Best / paranoid CVSS score: 8.7

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).