[CVE-2026-74543][LOW] net: udp_tunnel: fix memory leak in udp_tunnel_nic_unregister() [ Upstream

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

CVE: CVE-2026-74543
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: udp_tunnel: fix memory leak in udp_tunnel_nic_unregister() [ Upstream
Commit: b712da45bd9b9835d132e9fbc0c3e43c164cb1fd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b712da45bd9b9835d132e9fbc0c3e43c164cb1fd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74543
Analysis date: Sat, 15 Aug 2026 13:38:41 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74543 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74543

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-2026-74543	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A memory leak in the UDP tunnel NIC offload unregister path can occur when netdevice registration fails after NETDEV_REGISTER queued synchronization work. The cleanup path returned early while work was pending, and failed registrations do not get a later unregister rebroadcast, so the allocated udp_tunnel_nic object can remain permanently leaked. This is a resource exhaustion issue rather than a use after free or arbitrary memory corruption primitive. For the CVSS the PR:L is used in the paranoid score because delegated CAP_NET_ADMIN or container network administration may allow a less than fully privileged local actor to trigger netdevice registration failure paths repeatedly. The issue is not directly network reachable and requires local control over network device setup or a kernel path that registers such devices. Impact is denial of service through sustained memory exhaustion, with no supported confidentiality or integrity impact from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	REMOTE DEADLOCK INIT LEAK NETWORK HARDWARE SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

1. ActionableScore
* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Triggering failed netdevice registration paths usually requires privileged network device management.
* Availability impact realistic: +1 in the paranoid interpretation. Repeated leaks could eventually contribute to memory exhaustion, but the leaked object is small and the impact requires sustained triggering.
* Local unprivileged trigger: +1 only in the paranoid interpretation if delegated CAP_NET_ADMIN, container network administration, or a reduced-privilege network-management service can repeatedly reach this path.
* No generic memory corruption. The patch fixes a permanent leak of struct udp_tunnel_nic, not UAF, double free, OOB write, stale callback, or object reuse.
* No privilege escalation plausible. The leaked object is not freed and then reused, and the patch does not indicate attacker-controlled reclaim or corruption.

3. Reachability analysis
The realistic trigger is local and privileged through netdevice registration and unregister error paths. It is not directly network reachable and is not part of packet parsing. Namespaces or containers matter only if an untrusted actor has delegated network administration rights sufficient to create affected devices and force registration failure. The affected code is in networking infrastructure, but the vulnerable path is a control-plane cleanup path rather than a common receive or transmit data path.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like resource leak. The theoretical impact is sustained memory exhaustion, but the patch and commit message support only a memory leak, not memory corruption or LPE. Conservative handling can auto-close in many environments where only trusted administrators can manage netdevices. Paranoid handling keeps a small score because delegated CAP_NET_ADMIN could make repeated triggering more practical.

5. One-sentence report phrase
A memory leak in udp_tunnel_nic_unregister can permanently leak udp_tunnel_nic objects after failed netdevice registration when pending work caused cleanup to return early, requiring local network device management access and mainly posing sustained resource exhaustion risk.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. The patch supports a resource leak only, with no UAF, overwrite, stale pointer reuse, confidentiality impact, integrity impact, or direct network trigger.

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

Patch: net: udp_tunnel: fix memory leak in udp_tunnel_nic_unregister() [ Upstream
Commit: b712da45bd9b9835d132e9fbc0c3e43c164cb1fd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b712da45bd9b9835d132e9fbc0c3e43c164cb1fd

Changed files:
  net/ipv4/udp_tunnel_nic.c
  kernel/notifier.c
  net/core/dev.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=b712da45bd9b9835d132e9fbc0c3e43c164cb1fd

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

The original Linux kernel CVE announcement for CVE-2026-74543 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74543

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  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).