[CVE-2026-80866][LOW] tipc: avoid busy looping in tipc_exit_net() [ Upstream

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

CVE: CVE-2026-80866
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: tipc: avoid busy looping in tipc_exit_net() [ Upstream
Commit: 522d1d950b9e3b68190a6de7534827c8dccedb73
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=522d1d950b9e3b68190a6de7534827c8dccedb73
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80866
Analysis date: Fri, 04 Sep 2026 17:23:48 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like. Not an Actionable Moderate candidate
Manual review required: YES

Summary:
TIPC network namespace teardown can busy wait while pending UDP bearer cleanup work is outstanding, causing CPU consumption and possible soft lockups under specific scheduler or preemption conditions, with local reduced-privilege reachability possible only when TIPC and delegated network namespace control are available.

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

The original Linux kernel CVE announcement for CVE-2026-80866 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80866

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: 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-2026-80866	LOW	https://www.kernelcve.org/list/?q=CVE-2026-80866 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:U/C:N/I:N/A:H';**CWE-400;CWE-834;*CWE-835;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'TIPC net namespace teardown can busy wait in tipc_exit_net while waiting for pending UDP bearer cleanup work to finish. If cond_resched is ineffective, for example under CONFIG_PREEMPT_NONE or when netns exit runs in a high priority task, the loop can burn CPU for a long time and cause soft lockups. For the CVSS the PR:L is used because reliable triggering requires local control of TIPC or network namespace lifecycle, often through CAP_NET_ADMIN or container root rather than full host root. The issue is not directly network reachable because packet traffic alone does not trigger the vulnerable path. Impact is denial of service through CPU consumption and soft lockup, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Not an Actionable Moderate candidate (with actual score 2)	YES	DEADLOCK TIPC HARDWARE LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like. Not an Actionable Moderate candidate**::

## 2. Signal breakdown

* Reliable kernel crash / strong DoS: +1
  The patch addresses a busy-wait loop in `tipc_exit_net()` that can waste CPU and lead to soft lockups.

* Availability impact realistic: +1 in paranoid scoring only
  A soft lockup during network namespace teardown can degrade system responsiveness, but the impact is still DoS-only and not memory corruption.

* Local unprivileged trigger: +1 in paranoid scoring only
  This may be reachable from reduced-privilege environments if unprivileged user namespaces and delegated `CAP_NET_ADMIN` inside a network namespace are available. In typical host deployments it is not a plain unprivileged trigger.

* Hard or special condition required: -1
  The problematic behavior depends on pending UDP bearer cleanup work and conditions where `cond_resched()` is ineffective, such as `CONFIG_PREEMPT_NONE` or high-priority netns teardown.

No memory corruption, UAF, OOB access, information leak, privilege escalation, or cross-boundary policy bypass is shown by the patch.

## 3. Reachability analysis

The bug is triggered during TIPC network namespace teardown while waiting for pending UDP bearer cleanup work. It is not directly network reachable because packet traffic alone does not enter the vulnerable teardown wait path.

Typical triggering requires local control over TIPC setup and network namespace lifecycle, usually via `CAP_NET_ADMIN`, container root, or a privileged network management context. Namespace delegation can reduce the practical privilege level compared with full host root, but this still is not a normal remote or unprivileged local data-plane bug.

TIPC is not a universally enabled/default attack surface on many systems, and the problematic busy loop also depends on scheduler/preemption behavior. Realistic exploitation is therefore mainly local DoS under specific runtime conditions.

Call-site confidence: high, because both the waiting path in `tipc_exit_net()` and the wakeup path in `cleanup_bearer()` are visible in the provided patch.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like DoS issue rather than an Important-class kernel vulnerability. The realistic impact is CPU consumption and soft lockup during namespace teardown. There is no evidence of memory corruption, attacker-controlled object reuse, sensitive data exposure, privilege escalation, or remote protocol parsing reachability.

The paranoid score is only slightly higher because namespace delegation may make the trigger available to less-than-host-root actors in some environments.

## 5. One-sentence report phrase

TIPC network namespace teardown can busy wait while pending UDP bearer cleanup work is outstanding, causing CPU consumption and possible soft lockups under specific scheduler or preemption conditions, with local reduced-privilege reachability possible only when TIPC and delegated network namespace control are available.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a DoS-only busy-wait fix with no supported memory corruption or privilege escalation primitive. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

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

Patch: tipc: avoid busy looping in tipc_exit_net() [ Upstream
Commit: 522d1d950b9e3b68190a6de7534827c8dccedb73
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=522d1d950b9e3b68190a6de7534827c8dccedb73

Changed files:
  net/tipc/core.c
  net/tipc/udp_media.c
  net/sock.h
  net/ip.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=522d1d950b9e3b68190a6de7534827c8dccedb73

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

The original Linux kernel CVE announcement for CVE-2026-80866 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80866

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:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 1
  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).