CVE-2025-21816

System hang via offline-CPU timer enqueue

Published Feb 27, 2025 · Updated May 23, 2026

A high-resolution timer flaw in Linux 6.7 allows local users to cause a system hang during CPU hotplug operations. The hrtimer enqueue path can select the current CPU after it has gone offline, leaving a newly armed bandwidth or deadline timer queued there and ignored. Reaching the flaw requires local low-privileged access and a CPU-offline transition; the lost timer can stall kernel forward progress without disclosing or modifying data.

CVSS severity5.5
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A high-resolution timer flaw in Linux 6.7 allows local users to cause a system hang during CPU hotplug operations. The hrtimer enqueue path can select the current CPU after it has gone offline, leaving a newly armed bandwidth or deadline timer queued there and ignored. Reaching the flaw requires local low-privileged access and a CPU-offline transition; the lost timer can stall kernel forward progress without disclosing or modifying data.

The record

CVE
CVE-2025-21816
Published
Feb 27, 2025
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 2025CVE publishedPublication date reported by the CVE source.
  2. May 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=4.19.302 <4.20
  2. Affected versionversion=5.10.204 <5.11
  3. Affected versionversion=5.15.143 <5.16
  4. Affected versionversion=53f408cad05bb987af860af22f4151e5a18e6ee8 <63815bef47ec25f5a125019ca480882481ee1553
  5. Affected versionversion=5.4.264 <5.5
  6. Affected versionversion=54d0d83a53508d687fd4a225f8aa1f18559562d0
  7. Affected versionversion=5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 <2aecec58e9040ce3d2694707889f9914a2374955
  8. Affected versionversion=5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 <53dac345395c0d2493cbc2f4c85fe38aef5b63f5
  9. Affected versionversion=5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 <e456a88bddae4030ba962447bb84be6669f2a0c1
  10. Affected versionversion=6.1.68 <6.1.141
  11. Affected versionversion=6.6.7 <6.6.93
  12. Affected versionversion=6.7
  13. Affected versionversion=6fcbcc6c8e52650749692c7613cbe71bf601670d
  14. Affected versionversion=75b5016ce325f1ef9c63e5398a1064cf8a7a7354 <82ac6adbbb2aad14548a71d5e2e37f4964a15e38
  15. Affected versionversion=7f4c89400d2997939f6971c7981cc780a219e36b
  16. Affected versionversion=9a2fc41acb69dd4e2a58d0c04346c3333c2341fc

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.19.302 <4.20; version=5.10.204 <5.11; version=5.15.143 <5.16; version=53f408cad05bb987af860af22f4151e5a18e6ee8 <63815bef47ec25f5a125019ca480882481ee1553; version=5.4.264 <5.5; version=54d0d83a53508d687fd4a225f8aa1f18559562d0; version=5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 <2aecec58e9040ce3d2694707889f9914a2374955; version=5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 <53dac345395c0d2493cbc2f4c85fe38aef5b63f5; version=5c0930ccaad5a74d74e8b18b648c5eb21ed2fe94 <e456a88bddae4030ba962447bb84be6669f2a0c1; version=6.1.68 <6.1.141; version=6.6.7 <6.6.93; version=6.7; version=6fcbcc6c8e52650749692c7613cbe71bf601670d; version=75b5016ce325f1ef9c63e5398a1064cf8a7a7354 <82ac6adbbb2aad14548a71d5e2e37f4964a15e38; version=7f4c89400d2997939f6971c7981cc780a219e36b; version=9a2fc41acb69dd4e2a58d0c04346c3333c2341fc

Published CVSS scores

5.5SUSECVSS:3.1/AV:L/AC:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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