# CVE-2026-80866: tipc: avoid busy looping in tipc_exit_net()

> A busy-wait loop in the Linux kernel TIPC module can cause CPU exhaustion and soft lockups during network namespace exit, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-99459, BELL-CVE-2026-80866, DEBIAN-CVE-2026-80866, GHSA-8w3x-69pj-572x, UBUNTU-CVE-2026-80866

## What is CVE-2026-80866?

CVE-2026-80866 is a denial of service vulnerability in Linux, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

tipc: avoid busy looping in tipc_exit_net()

Blamed commit introduced a busy-wait loop in tipc_exit_net()
to wait for pending UDP bearer cleanup works to complete:

       while (atomic_read(&tn->wq_count))
               cond_resched();

This loop can busy-wait for a long time if cond_resched() is a NOP. This
typically happens if the netns exit is executed by a high priority task,
or under kernels configured without preemption (CONFIG_PREEMPT_NONE). In
such cases, it wastes CPU cycles and can lead to soft lockups.

Fix this by replacing the busy loop with wait_var_event(), allowing the
thread to sleep properly until the work queue count reaches zero.

Accordingly, update cleanup_bearer() to use atomic_dec_and_test() and
wake_up_var() to wake up the waiter when the count drops to zero.

This uses the global wait queue hash table, avoiding the need to bloat
struct tipc_net with a wait_queue_head_t. The atomic_dec_and_test()
provides the necessary memory barrier to ensure the wakeup is not missed.

## Which versions are affected by CVE-2026-80866?


## How do I fix CVE-2026-80866?

Apply the vendor's patch.

## Is CVE-2026-80866 being exploited?

There is no known exploitation of CVE-2026-80866 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80866 and fix it if it is affected.

What it is: CVE-2026-80866 is a denial of service vulnerability in Linux, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-80866 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-80866/ (Markdown: https://insights.sbomify.com/CVE-2026-80866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80866
- OSV: https://osv.dev/vulnerability/CVE-2026-80866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80866/
Summaries are generated and may contain mistakes; the official description above is the record.