[CVE-2026-72052][IMPORTANT] net: ip6_gre: require CAP_NET_ADMIN in the device netns for changelink

[CVE-2026-72052][IMPORTANT] net: ip6_gre: require CAP_NET_ADMIN in the device netns for changelink

[AL-KERNEL]

CVE: CVE-2026-72052
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net: ip6_gre: require CAP_NET_ADMIN in the device netns for changelink
Commit: 129f8939e5af683cec3a1a5edcb40a64636ad81e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=129f8939e5af683cec3a1a5edcb40a64636ad81e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72052
Analysis date: Sat, 15 Aug 2026 14:16:36 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
`ip6_gre and ip6erspan changelink authorization checked CAP_NET_ADMIN only in the device namespace, allowing a caller with delegated network capability in one namespace to rewrite tunnel configuration owned by another namespace, causing a cross-namespace network policy bypass with possible traffic redirection or disruption.`

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

The original Linux kernel CVE announcement for CVE-2026-72052 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72052

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-2026-72052	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:H/I:H/A:H';CWE-862;CWE-863;CWE-266;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:H/A:L';BEST CVSS score: '8.8';DESCR 'ip6_gre changelink authorization was incomplete because the rtnl path checked CAP_NET_ADMIN only in dev_net(dev), while the tunnel object can belong to a different link netns. A caller with CAP_NET_ADMIN in the device namespace but not in the tunnel link namespace could rewrite ip6gre or ip6erspan tunnel configuration across a namespace boundary. For the CVSS the PR:L is used because the attacker needs local capability in one network namespace, but does not need full host root or CAP_NET_ADMIN in the protected tunnel namespace. The issue is not directly network reachable and is triggered through local rtnetlink control plane operations. Impact is an authorization bypass with possible traffic redirection, tunnel disruption, or policy bypass. For the paranoid score, choose the highest still-defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';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, allowing a caller privileged in `dev_net(dev)` but not in `t->net` to modify tunnel state across a namespace boundary.

* **Cross-boundary isolation/policy bypass: +1**
  This is a network namespace authorization bypass affecting objects owned by another namespace.

* **Integrity impact plausible: +1**
  Rewriting IPv6 GRE or ERSPAN tunnel parameters can alter routing, tunnel endpoints, encapsulation behavior, or network policy.

* **Availability impact realistic: +1**
  Unauthorized tunnel modification can break connectivity or disrupt encapsulated traffic.

* **Requires CAP_NET_ADMIN in one namespace: -0/-1 interpreted conservatively**
  This is not full host-root equivalence because the attacker lacks `CAP_NET_ADMIN` in the protected tunnel namespace. Conservative scoring effectively treats this as reduced-privilege namespace capability, not full admin.

Paranoid additional signals:

* **Confidentiality impact plausible: +1**
  If tunnel endpoint or ERSPAN/GRE configuration can be redirected, traffic exposure or mirroring impact is plausible in some deployments.

* **Practical exploit chain strongly implied: +1**
  The commit directly describes the chain: device and tunnel link netns differ, rtnl checks only one namespace, and the caller can rewrite a tunnel living in another namespace.

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

## 3. Reachability analysis

Triggering requires local rtnetlink control-plane access plus `CAP_NET_ADMIN` in the device namespace. It does not require `CAP_NET_ADMIN` in the tunnel link namespace, which is the core security failure. This matters for containers, delegated network namespaces, reduced-capability root, and orchestration setups where one namespace may be less trusted than another.

The issue is **not directly network reachable** through packet traffic. It requires control-plane operations such as `changelink` on `ip6gre` or `ip6erspan` devices. The path is not universal default exposure, but network namespaces and GRE/ERSPAN tunnels are common enough in containerized and virtualized networking that this should not be auto-closed as a niche correctness issue.

## 4. Severity interpretation

This behaves like an **Actionable Moderate at minimum**, with a defensible **Strong Important candidate** interpretation in namespace-heavy deployments.

There is no realistic evidence of kernel memory corruption or direct code execution. The important part is the authorization bypass: a process with limited network capability in one namespace can affect tunnel configuration belonging to another namespace. Realistic impact is policy bypass, traffic disruption, and possibly traffic redirection or exposure depending on tunnel use.

## 5. One-sentence report phrase

`ip6_gre and ip6erspan changelink authorization checked CAP_NET_ADMIN only in the device namespace, allowing a caller with delegated network capability in one namespace to rewrite tunnel configuration owned by another namespace, causing a cross-namespace network policy bypass with possible traffic redirection or disruption.`

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

This should be manually reviewed because it is a namespace capability bypass, not a simple privileged-only configuration bug. The practical severity depends heavily on whether untrusted containers or delegated network administrators can operate on moved `ip6gre` or `ip6erspan` devices.

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

Patch: net: ip6_gre: require CAP_NET_ADMIN in the device netns for changelink
Commit: 129f8939e5af683cec3a1a5edcb40a64636ad81e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=129f8939e5af683cec3a1a5edcb40a64636ad81e

Commit description:

ip6gre_changelink() and ip6erspan_changelink() operate 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 both ops on rtnl_dev_link_net_capable() at their top, before any
attribute is parsed.

Reported-by: Xiao Liang <shaw.leon@gmail.com>
Closes: https://lore.kernel.org/netdev/CABAhCOSzP1vaThGV35_VnsRCb=87_CPjPVsTHbq905k8A+BuUg@mail.gmail.com/
Fixes: 690afc1 ("net: ip6_gre: fix moving ip6gre between namespaces")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260612085941.3158249-6-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/ip6_gre.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=129f8939e5af683cec3a1a5edcb40a64636ad81e

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

The original Linux kernel CVE announcement for CVE-2026-72052 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72052

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: 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).