[CVE-2026-72127][LOW] netdev-genl: report NAPI thread PID in the caller's pid namespace

[CVE-2026-72127][LOW] netdev-genl: report NAPI thread PID in the caller's pid namespace

[AL-KERNEL]

CVE: CVE-2026-72127
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netdev-genl: report NAPI thread PID in the caller's pid namespace
Commit: fb18095389fe81f140d39585a2624aca9d42227e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb18095389fe81f140d39585a2624aca9d42227e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72127
Analysis date: Sat, 15 Aug 2026 08:14:40 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72127 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72127

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72127	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:N/A:N';*CWE-200;CWE-668;CWE-497;BEST CVSS score: '3.3';DESCR 'NETDEV_CMD_NAPI_GET can expose the global PID of a NAPI kthread to a caller running in a child PID namespace because netdev_nl_napi_fill_one used task_pid_nr instead of translating the PID into the callers namespace. The leaked value identifies a kernel thread PID from the initial PID namespace even though that task is not visible inside the caller namespace, where the expected value is 0. For the CVSS the PR:L is used because triggering requires a local process context able to issue the netdev generic netlink request, but no administrative permission is required by this command. The issue is not network reachable through packet traffic and does not involve memory corruption. Impact is limited confidentiality loss through namespace information exposure, with no integrity or availability impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE SIMPLEFIX LINUS IO_URING  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: same
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. NETDEV_CMD_NAPI_GET lacks GENL_ADMIN_PERM and can be issued by a local caller in a child PID namespace.
* Confidentiality impact plausible: +1. The bug leaks the initial PID namespace value of a NAPI kthread PID into a namespace where that task should not be visible.
* Cross-boundary security bypass: +0. This is a namespace isolation correctness issue, but the leaked object is only a kernel thread PID, not a sensitive file descriptor, credential, socket, ptrace target, or privileged process state.
* Memory corruption: +0. No UAF, OOB access, stale pointer, write primitive, or refcount/lifetime corruption is shown.
* Reliable DoS: +0. No crash, hang, or resource exhaustion is indicated.

3. Reachability analysis
A local process in a child PID namespace can query the netdev generic netlink interface and receive NETDEV_A_NAPI_PID. No administrative permission is required for this command, but local code execution is required, so this is not PR:N in CVSS terms. The issue is not reachable through network packet traffic. Containers and PID namespaces matter because the bug violates expected PID namespace translation, but the practical leak is low-value.

4. Severity interpretation
This behaves like a low-severity information disclosure / namespace isolation bug, not an actionable Moderate or Important kernel vulnerability. The theoretical security issue is that a caller sees a global PID that should be hidden, but there is no evidence of memory corruption, privilege escalation, fd theft, credential exposure, or DoS. Realistic exploitation value is limited to minor host namespace information disclosure.

5. One-sentence report phrase
NETDEV_CMD_NAPI_GET could expose a NAPI kthread global PID to a caller in a child PID namespace because the PID was reported with task_pid_nr instead of being translated into the callers namespace.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The patch fixes a limited PID namespace information leak with no memory corruption, no network-triggered path, no DoS, and no plausible privilege escalation primitive.

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

Patch: netdev-genl: report NAPI thread PID in the caller's pid namespace
Commit: fb18095389fe81f140d39585a2624aca9d42227e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb18095389fe81f140d39585a2624aca9d42227e

Commit description:

netdev_nl_napi_fill_one() reports the NAPI kthread PID in NETDEV_A_NAPI_PID
using task_pid_nr(), which returns the PID in the initial pid namespace.

NETDEV_CMD_NAPI_GET does not have GENL_ADMIN_PERM and the netdev genl family
is netnsok, so a caller in a child pid namespace can issue it. That caller
then sees the kthread's global PID, even though the kthread is not visible
in its pid namespace, where the value should be 0.

Translate the PID through the caller's pid namespace, the same way commit
3799c25 ("io_uring/fdinfo: translate SqThread PID through caller's
pid_ns") did for the io_uring SQPOLL thread. The doit and dumpit paths both
run synchronously in the caller's context, so task_active_pid_ns(current) is
the caller's pid namespace.

Fixes: db4704f ("netdev-genl: Add PID for the NAPI thread")
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Joe Damato <joe@dama.to>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Link: https://patch.msgid.link/20260615171736.1709318-1-maoyixie.tju@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/core/netdev-genl.c
  net/busy_poll.h
  net/net_namespace.h

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=fb18095389fe81f140d39585a2624aca9d42227e

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

The original Linux kernel CVE announcement for CVE-2026-72127 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72127

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 3.3

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).