# CVE-2026-90066: samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify

> A null pointer dereference in the Linux kernel ftrace sample module can cause a system crash during module unload if thread creation fails.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102860, BELL-CVE-2026-90066, DEBIAN-CVE-2026-90066, GHSA-h42m-cfhq-9g8c, UBUNTU-CVE-2026-90066

## What is CVE-2026-90066?

CVE-2026-90066 is a vulnerability in Linux, published on 17 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:

samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify

ftrace_direct_multi_init() assigns kthread_run()'s return value to
simple_tsk without an IS_ERR() check. When kthread_run() fails it
returns ERR_PTR(-ENOMEM), but init still returns 0, so the module loads
with simple_tsk holding an error pointer. On unload,
ftrace_direct_multi_exit() then passes that ERR_PTR to kthread_stop(),
leading to a null-pointer-dereference.

Check the return value of kthread_run() with IS_ERR(); on failure,
unregister the ftrace direct call and propagate the error code.

## Which versions are affected by CVE-2026-90066?


## How do I fix CVE-2026-90066?

Apply the vendor's patch.

## Is CVE-2026-90066 being exploited?

There is no known exploitation of CVE-2026-90066 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90066 and fix it if it is affected.

What it is: CVE-2026-90066 is a vulnerability in Linux, published on 17 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-2026-90066 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-2026-90066/ (Markdown: https://insights.sbomify.com/CVE-2026-90066/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90066
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90066
- OSV: https://osv.dev/vulnerability/CVE-2026-90066

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90066/
Summaries are generated and may contain mistakes; the official description above is the record.