# CVE-2025-21655: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

> A use-after-free vulnerability in the Linux kernel's io_uring eventfd handling allows attackers to potentially execute arbitrary code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 20 Jan 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-21655, DEBIAN-CVE-2025-21655, GHSA-vwm2-fvjj-vcv3, UBUNTU-CVE-2025-21655

## What is CVE-2025-21655?

CVE-2025-21655 is a high-severity use after free vulnerability in Linux kernel, published on 20 Jan 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:

io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

io_eventfd_do_signal() is invoked from an RCU callback, but when
dropping the reference to the io_ev_fd, it calls io_eventfd_free()
directly if the refcount drops to zero. This isn't correct, as any
potential freeing of the io_ev_fd should be deferred another RCU grace
period.

Just call io_eventfd_put() rather than open-code the dec-and-test and
free, which will correctly defer it another RCU grace period.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-21655?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21655?

Apply the vendor's patch.

## Is CVE-2025-21655 being exploited?

There is no known exploitation of CVE-2025-21655 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-2025-21655 and fix it if it is affected.

What it is: CVE-2025-21655 is a high-severity use after free vulnerability in Linux kernel, published on 20 Jan 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-2025-21655 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-2025-21655/ (Markdown: https://insights.sbomify.com/CVE-2025-21655/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21655
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21655
- OSV: https://osv.dev/vulnerability/CVE-2025-21655

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21655/
Summaries are generated and may contain mistakes; the official description above is the record.