# CVE-2025-40260: sched_ext: Fix scx_enable() crash on helper kthread creation failure

> A local attacker with low privileges can cause a kernel crash by triggering a specific error path in sched_ext, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40260, DEBIAN-CVE-2025-40260, GHSA-3f36-x6r9-r53h, UBUNTU-CVE-2025-40260

## What is CVE-2025-40260?

CVE-2025-40260 is a vulnerability in Linux, published on 4 Dec 2025. 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:

sched_ext: Fix scx_enable() crash on helper kthread creation failure

A crash was observed when the sched_ext selftests runner was
terminated with Ctrl+\ while test 15 was running:

NIP [c00000000028fa58] scx_enable.constprop.0+0x358/0x12b0
LR [c00000000028fa2c] scx_enable.constprop.0+0x32c/0x12b0
Call Trace:
scx_enable.constprop.0+0x32c/0x12b0 (unreliable)
bpf_struct_ops_link_create+0x18c/0x22c
__sys_bpf+0x23f8/0x3044
sys_bpf+0x2c/0x6c
system_call_exception+0x124/0x320
system_call_vectored_common+0x15c/0x2ec

kthread_run_worker() returns an ERR_PTR() on failure rather than NULL,
but the current code in scx_alloc_and_add_sched() only checks for a NULL
helper. Incase of failure on SIGQUIT, the error is not handled in
scx_alloc_and_add_sched() and scx_enable() ends up dereferencing an
error pointer.

Error handling is fixed in scx_alloc_and_add_sched() to propagate
PTR_ERR() into ret, so that scx_enable() jumps to the existing error
path, avoiding random dereference on failure.

## Which versions are affected by CVE-2025-40260?


## How do I fix CVE-2025-40260?

Apply the vendor's patch.

## Is CVE-2025-40260 being exploited?

There is no known exploitation of CVE-2025-40260 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40260 and fix it if it is affected.

What it is: CVE-2025-40260 is a vulnerability in Linux, published on 4 Dec 2025. 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-2025-40260 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-2025-40260/ (Markdown: https://insights.sbomify.com/CVE-2025-40260/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40260
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40260
- OSV: https://osv.dev/vulnerability/CVE-2025-40260

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40260/
Summaries are generated and may contain mistakes; the official description above is the record.