# CVE-2025-39745: rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels

> A bug in the Linux kernel's RCU torture test module causes a kernel warning splat on RT kernels, potentially leading to system instability or denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 11 Sep 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-39745, GHSA-59f6-f4pc-ww92, ROOT-OS-DEBIAN-12-CVE-2025-39745, ROOT-OS-DEBIAN-13-CVE-2025-39745, ROOT-OS-UBUNTU-2204-CVE-2025-39745, ROOT-OS-UBUNTU-2404-CVE-2025-39745, UBUNTU-CVE-2025-39745

## What is CVE-2025-39745?

CVE-2025-39745 is a medium-severity denial of service vulnerability in Linux kernel, published on 11 Sep 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:

rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels

For built with CONFIG_PREEMPT_RT=y kernels, running rcutorture
tests resulted in the following splat:

[   68.797425] rcutorture_one_extend_check during change: Current 0x1  To add 0x1  To remove 0x0  preempt_count() 0x0
[   68.797533] WARNING: CPU: 2 PID: 512 at kernel/rcu/rcutorture.c:1993 rcutorture_one_extend_check+0x419/0x560 [rcutorture]
[   68.797601] Call Trace:
[   68.797602]  <TASK>
[   68.797619]  ? lockdep_softirqs_off+0xa5/0x160
[   68.797631]  rcutorture_one_extend+0x18e/0xcc0 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797646]  ? local_clock+0x19/0x40
[   68.797659]  rcu_torture_one_read+0xf0/0x280 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797678]  ? __pfx_rcu_torture_one_read+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797804]  ? __pfx_rcu_torture_timer+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797815] rcu-torture: rcu_torture_reader task started
[   68.797824] rcu-torture: Creating rcu_torture_reader task
[   68.797824]  rcu_torture_reader+0x238/0x580 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c]
[   68.797836]  ? kvm_sched_clock_read+0x15/0x30

Disable BH does not change the SOFTIRQ corresponding bits in
preempt_count() for RT kernels, this commit therefore use
softirq_count() to check the if BH is disabled.

## Which versions are affected by CVE-2025-39745?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39745?

Apply the vendor's patch.

## Is CVE-2025-39745 being exploited?

There is no known exploitation of CVE-2025-39745 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39745 and fix it if it is affected.

What it is: CVE-2025-39745 is a medium-severity denial of service vulnerability in Linux kernel, published on 11 Sep 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-2025-39745 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2025-39745/ (Markdown: https://insights.sbomify.com/CVE-2025-39745/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39745
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39745
- OSV: https://osv.dev/vulnerability/CVE-2025-39745

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39745/
Summaries are generated and may contain mistakes; the official description above is the record.