[CVE-2026-53075][MODERATE 7.0] ppp: require CAP_NET_ADMIN in target netns for unattached ioctls [ Upstream

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

CVE: CVE-2026-53075
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ppp: require CAP_NET_ADMIN in target netns for unattached ioctls [ Upstream
Commit: c9edd90c57ae23692fff6b049fdfa4572a9fd532
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9edd90c57ae23692fff6b049fdfa4572a9fd532
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53075
Analysis date: Wed, 24 Jun 2026 13:24:13 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Treat as **Actionable Moderate at minimum**, with **Important-candidate manual review** because it is a local capability and namespace boundary bypass.
Manual review required: YES

Summary:
A local unprivileged user with unprivileged user namespaces enabled may gain CAP_NET_ADMIN only in a new user namespace and still issue PPP administrative ioctls against an inherited target network namespace, bypassing the intended capability check and potentially altering or disrupting PPP network state.

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

The original Linux kernel CVE announcement for CVE-2026-53075 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53075

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53075	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H';CWE-863;CWE-269;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '7.3';DESCR 'PPP unattached administrative ioctls used a capability check that could be satisfied in a different user namespace than the one owning the target network namespace. A local unprivileged user can create a new user namespace, gain CAP_NET_ADMIN only there, and still operate on an inherited network namespace through PPPIOCNEWUNIT, PPPIOCATTACH, or PPPIOCATTCHAN. For the CVSS the PR:L is used for the paranoid score because local code execution by an unprivileged user is enough when unprivileged user namespaces are enabled. The issue is not network reachable and is triggered through the local /dev/ppp control interface. Impact is an authorization bypass for PPP administrative operations, with possible network configuration integrity impact and denial of service in the target netns.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	SIMPLEFIX NETWORK LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **6**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Treat as **Actionable Moderate at minimum**, with **Important-candidate manual review** because it is a local capability and namespace boundary bypass.

## 2. Signal breakdown

Triggered signals:

* **Local unprivileged trigger: +1**
  A local unprivileged user can create a new user namespace with `CLONE_NEWUSER` and obtain `CAP_NET_ADMIN` only inside that new user namespace.

* **Security-boundary bypass with practical sensitive-object access: +2**
  The bug bypasses the intended `CAP_NET_ADMIN` check for the user namespace owning the target network namespace. This is a capability and namespace permission-model bypass.

* **Cross-boundary isolation/policy bypass: +1**
  The vulnerable behavior lets a userns-only privileged process affect an inherited network namespace where it should not have administrative authority.

* **Practical exploit chain strongly implied: +1**
  The commit directly describes the chain: create user namespace, gain local `CAP_NET_ADMIN` there, then issue unattached PPP administrative ioctls against the inherited netns.

* **Integrity impact plausible: +1**
  Unauthorized PPP unit creation or attachment can alter network configuration state in the target netns.

* **Availability impact realistic: +1, paranoid only**
  Misuse of PPP administrative ioctls may disrupt PPP networking or consume/control PPP units in the target netns. This is plausible but not demonstrated as a strong system-wide DoS.

Negative or non-triggered signals:

* **Remote reachable: +0**
  This is a local `/dev/ppp` ioctl path, not packet-triggered.

* **Memory corruption / UAF / OOB / arbitrary write: +0**
  The patch is an authorization check. No memory corruption primitive is shown.

* **Requires admin/root/CAP_NET_ADMIN penalty: 0**
  Do not apply the full `-2` penalty because the vulnerability is specifically that the required capability is checked in the wrong namespace and can be bypassed by an unprivileged user when unprivileged user namespaces are enabled.

* **Rare subsystem/configuration: optional -1 not applied to paranoid score**
  PPP is less common than core TCP/IP, and `/dev/ppp` access/module availability affects exposure. This supports the lower conservative score but should not auto-close the issue.

## 3. Reachability analysis

The bug is triggered locally through unattached PPP administrative ioctls such as `PPPIOCNEWUNIT`, `PPPIOCATTACH`, or `PPPIOCATTCHAN`. A realistic attacker needs local code execution and access to `/dev/ppp`. If unprivileged user namespaces are enabled, the attacker can create a new user namespace, gain `CAP_NET_ADMIN` only there, and abuse the mismatch between the file credential namespace and the target network namespace.

Containers and delegated namespaces matter significantly. A container root or reduced-capability service account may not have real `CAP_NET_ADMIN` in the host or parent netns, but the bug may let it perform PPP operations against an inherited target netns. This is why the issue should not be treated as requiring full host-root privileges.

The path is not remotely reachable over the network. Exposure depends on whether PPP support and `/dev/ppp` are available and whether unprivileged user namespaces are enabled.

## 4. Severity interpretation

This is not a memory-corruption vulnerability and does not by itself show privilege escalation to root or arbitrary kernel code execution. It behaves as a **local authorization bypass across namespace and capability boundaries**.

Realistically, the demonstrated impact is unauthorized PPP administrative control in a target network namespace. That supports **Actionable Moderate** handling. The paranoid score reaches the lower **Important-candidate** range because capability-boundary bypasses in namespace-aware kernel code can have deployment-specific consequences, especially in containerized or reduced-capability environments.

## 5. One-sentence report phrase

A local unprivileged user with unprivileged user namespaces enabled may gain CAP_NET_ADMIN only in a new user namespace and still issue PPP administrative ioctls against an inherited target network namespace, bypassing the intended capability check and potentially altering or disrupting PPP network state.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

This is a capability and namespace security-boundary bypass, not a simple DoS or cleanup bug. Manual review is needed to determine whether the affected deployment exposes `/dev/ppp`, enables unprivileged user namespaces, or relies on containers or reduced-capability users as a security boundary.

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

Patch: ppp: require CAP_NET_ADMIN in target netns for unattached ioctls [ Upstream
Commit: c9edd90c57ae23692fff6b049fdfa4572a9fd532
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c9edd90c57ae23692fff6b049fdfa4572a9fd532

Changed files:
  drivers/net/ppp/ppp_generic.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=c9edd90c57ae23692fff6b049fdfa4572a9fd532

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

The original Linux kernel CVE announcement for CVE-2026-53075 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53075

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:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H
  The Best / paranoid CVSS score: 7.3

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).