# CVE-2025-21655

## Summary

- **CVE ID:** CVE-2025-21655
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Jan 20, 2025
- **Last Modified:** Sep 8, 2026

## 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.

## Affected Products

- Linux — Linux (21a091b970cdbcf3e8ff829234b51be6f9192766)
- Linux — Linux (6.1)
- Linux — Linux (0)
- Linux — Linux (6.1.125)
- Linux — Linux (6.6.72)
- Linux — Linux (6.12.10)
- Linux — Linux (6.13)

## References

- [CNA](https://git.kernel.org/stable/c/6b63308c28987c6010b1180c72a6db4df6c68033)
- [CNA](https://git.kernel.org/stable/c/8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10)
- [CNA](https://git.kernel.org/stable/c/a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7)
- [CNA](https://git.kernel.org/stable/c/c9a40292a44e78f71258b8522655bffaf5753bdb)
- [CNA](https://project-zero.issues.chromium.org/issues/388499293)
- [CVE](https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.25%
- **EPSS Percentile:** 16.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._