# CVE-2025-40142: ALSA: pcm: Disable bottom softirqs as part of spin_lock_irq() on PREEMPT_RT

> A race condition in the Linux kernel ALSA PCM driver on PREEMPT_RT systems can cause a deadlock, 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:** 12 Nov 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40142, DEBIAN-CVE-2025-40142, GHSA-5f4r-vh38-xfwr, ROOT-OS-DEBIAN-13-CVE-2025-40142, UBUNTU-CVE-2025-40142

## What is CVE-2025-40142?

CVE-2025-40142 is a vulnerability in Linux, published on 12 Nov 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:

ALSA: pcm: Disable bottom softirqs as part of spin_lock_irq() on PREEMPT_RT

snd_pcm_group_lock_irq() acquires a spinlock_t and disables interrupts
via spin_lock_irq(). This also implicitly disables the handling of
softirqs such as TIMER_SOFTIRQ.
On PREEMPT_RT softirqs are preemptible and spin_lock_irq() does not
disable them. That means a timer can be invoked during spin_lock_irq()
on the same CPU. Due to synchronisations reasons local_bh_disable() has
a per-CPU lock named softirq_ctrl.lock which synchronizes individual
softirq against each other.
syz-bot managed to trigger a lockdep report where softirq_ctrl.lock is
acquired in hrtimer_cancel() in addition to hrtimer_run_softirq(). This
is a possible deadlock.

The softirq_ctrl.lock can not be made part of spin_lock_irq() as this
would lead to too much synchronisation against individual threads on the
system. To avoid the possible deadlock, softirqs must be manually
disabled before the lock is acquired.

Disable softirqs before the lock is acquired on PREEMPT_RT.

## Which versions are affected by CVE-2025-40142?


## How do I fix CVE-2025-40142?

Apply the vendor's patch.

## Is CVE-2025-40142 being exploited?

There is no known exploitation of CVE-2025-40142 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40142 and fix it if it is affected.

What it is: CVE-2025-40142 is a vulnerability in Linux, published on 12 Nov 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-2025-40142 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-2025-40142/ (Markdown: https://insights.sbomify.com/CVE-2025-40142/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40142
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40142
- OSV: https://osv.dev/vulnerability/CVE-2025-40142

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40142/
Summaries are generated and may contain mistakes; the official description above is the record.