CVE-2025-21655

Local crash via premature io_uring eventfd free

Published Jan 20, 2025 · Updated Sep 8, 2026

A race condition in Linux kernel 6.1 through 6.13-rc6 allows local users to crash the system through io_uring eventfd handling. io_eventfd_do_signal() directly frees io_ev_fd when its reference count reaches zero inside an RCU callback instead of deferring release through another grace period. Low-privileged local access and a refcount-release race are required; Siemens also lists the flaw in affected controllers' GNU/Linux subsystem.

CVSS severity4.7
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A race condition in Linux kernel 6.1 through 6.13-rc6 allows local users to crash the system through io_uring eventfd handling. io_eventfd_do_signal() directly frees io_ev_fd when its reference count reaches zero inside an RCU callback instead of deferring release through another grace period. Low-privileged local access and a refcount-release race are required; Siemens also lists the flaw in affected controllers' GNU/Linux subsystem.

The record

CVE
CVE-2025-21655
Published
Jan 20, 2025
Updated
Sep 8, 2026
Vendor
Siemens
Product
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
Classifications
CWE-362, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 20, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=V3.1.6 <*

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Siemens · SIPLUS S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.6 <*
The Linux Kernel Organization · Linuxversion=21a091b970cdbcf3e8ff829234b51be6f9192766 <6b63308c28987c6010b1180c72a6db4df6c68033; version=21a091b970cdbcf3e8ff829234b51be6f9192766 <8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10; version=21a091b970cdbcf3e8ff829234b51be6f9192766 <a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7; version=21a091b970cdbcf3e8ff829234b51be6f9192766 <c9a40292a44e78f71258b8522655bffaf5753bdb; version=6.1
Siemens · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPversion=V3.1.6 <*
Siemens · SIMATIC S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.6 <*

Published CVSS scores

4.7Siemens ProductCERTCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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