[CVE-2026-72053][MODERATE 7.0] net: ipip: require CAP_NET_ADMIN in the device netns for changelink

[CVE-2026-72053][MODERATE 7.0] net: ipip: require CAP_NET_ADMIN in the device netns for changelink

[AL-KERNEL]

CVE: CVE-2026-72053
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: ipip: require CAP_NET_ADMIN in the device netns for changelink
Commit: 91571643e554ae89a91942380d5f5361fb7060a2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91571643e554ae89a91942380d5f5361fb7060a2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72053
Analysis date: Sun, 16 Aug 2026 05:44:48 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
IPIP changelink failed to require CAP_NET_ADMIN in the tunnel link namespace, allowing a caller with delegated network administration rights in another namespace to rewrite tunnel settings and potentially redirect or disrupt traffic.

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

The original Linux kernel CVE announcement for CVE-2026-72053 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72053

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 7.0
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-2026-72053	MODERATE	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-269;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L';BEST CVSS score: '8.8';DESCR 'IPIP changelink authorization was incomplete because the rtnl path checked CAP_NET_ADMIN only in dev_net(dev), while the tunnel link namespace t net could be different after device creation or movement across network namespaces. A caller with administrative capability in the device namespace but not in the tunnel link namespace could rewrite tunnel settings that should belong to another security boundary. For the CVSS the PR:L value is used because reliable triggering requires local netlink access plus CAP_NET_ADMIN in at least one relevant namespace, but not full host administrative privileges. The issue is not directly network reachable and is triggered through local rtnl control plane operations rather than packet traffic. Impact can include unauthorized tunnel reconfiguration, traffic disruption, and possible traffic redirection or exposure depending on how the IPIP tunnel is used.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE SIMPLEFIX NETWORK HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* 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 tunnel link namespace. A caller privileged in dev_net(dev) but not in t->net can modify a tunnel belonging to another namespace boundary.

* Cross-boundary isolation/policy bypass: +1
  This is explicitly a network namespace capability boundary issue.

* Confidentiality impact plausible: +1
  Unauthorized tunnel reconfiguration can plausibly redirect or expose tunneled traffic depending on the IPIP deployment.

* Integrity impact plausible: +1
  The attacker can change tunnel parameters without authorization in the tunnel link namespace.

* Availability impact realistic: +1
  Unauthorized tunnel changes can break routing or disrupt connectivity for the affected namespace.

Applied reduction:

* Requires CAP_NET_ADMIN in one namespace: -1 conservative only
  This is not fully unprivileged, but the full -2 admin penalty is not appropriate because the bug is the bypass of a different capability namespace boundary. Container root or delegated CAP_NET_ADMIN is weaker than full host root.

Conservative total: 5
Paranoid total: 6

## 3. Reachability analysis

The bug is reachable through local rtnl netlink changelink operations, not through packet traffic. The attacker needs CAP_NET_ADMIN in the device namespace but not in the tunnel link namespace. This can matter in containerized or namespace-delegated setups where a process is intentionally given limited network administration rights.

The path is not remote-network-triggerable by ordinary IPIP packets. It requires an existing or movable IPIP tunnel configuration where dev_net(dev) and t->net differ. This is configuration-dependent, but not merely theoretical because the patch exists specifically for x-netns IPIP behavior.

Call-site confidence: high. The patch is directly in ipip_changelink() and the commit message explains the exact missing authorization boundary.

## 4. Severity interpretation

This is not memory corruption and does not imply kernel code execution. It behaves as an access-control and namespace isolation bypass.

Realistically, this is at least an actionable Moderate issue because it allows unauthorized tunnel reconfiguration across a capability boundary. In sensitive container or multi-tenant networking deployments, it can approach Important severity because tunnel rewrites may affect traffic confidentiality, integrity, and availability outside the attackers intended namespace authority.

## 5. One-sentence report phrase

IPIP changelink failed to require CAP_NET_ADMIN in the tunnel link namespace, allowing a caller with delegated network administration rights in another namespace to rewrite tunnel settings and potentially redirect or disrupt traffic.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

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

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

Patch: net: ipip: require CAP_NET_ADMIN in the device netns for changelink
Commit: 91571643e554ae89a91942380d5f5361fb7060a2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91571643e554ae89a91942380d5f5361fb7060a2

Commit description:

ipip_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 ipip_changelink() on rtnl_dev_link_net_capable() at its 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: 6c742e7 ("ipip: add x-netns support")
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/20260612085941.3158249-3-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/ipip.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=91571643e554ae89a91942380d5f5361fb7060a2

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

The original Linux kernel CVE announcement for CVE-2026-72053 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72053

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:L/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: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).