CVE-2021-47512

Local denial of service via timer rearming

Published May 24, 2024 · Updated Aug 5, 2026

Denial of service in the Linux kernel 5.6 through 5.15.7 allows local users to stall a CPU by deleting a configured FQ-PIE qdisc. fq_pie_destroy() calls del_timer_sync() without first clearing tupdate, allowing fq_pie_timer() to rearm adapt_timer during teardown. Exploitation requires local access and the ability to configure and delete an FQ-PIE qdisc; the documented consequence is a kernel RCU stall.

CVSS severity5.5
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the Linux kernel 5.6 through 5.15.7 allows local users to stall a CPU by deleting a configured FQ-PIE qdisc. fq_pie_destroy() calls del_timer_sync() without first clearing tupdate, allowing fq_pie_timer() to rearm adapt_timer during teardown. Exploitation requires local access and the ability to configure and delete an FQ-PIE qdisc; the documented consequence is a kernel RCU stall.

The record

CVE
CVE-2021-47512
Published
May 24, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 24, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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=5.6
  2. Affected versionversion=ec97ecf1ebe485a17cd8395a5f35e6b80b57665a <2a51edaf5cc563574878b93d7ef3d5955dda7030
  3. Affected versionversion=ec97ecf1ebe485a17cd8395a5f35e6b80b57665a <61c2402665f1e10c5742033fce18392e369931d7
  4. Affected versionversion=ec97ecf1ebe485a17cd8395a5f35e6b80b57665a <d86216dfda7c98375f809e26a30bfdaaba21d46e

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.6; version=ec97ecf1ebe485a17cd8395a5f35e6b80b57665a <2a51edaf5cc563574878b93d7ef3d5955dda7030; version=ec97ecf1ebe485a17cd8395a5f35e6b80b57665a <61c2402665f1e10c5742033fce18392e369931d7; version=ec97ecf1ebe485a17cd8395a5f35e6b80b57665a <d86216dfda7c98375f809e26a30bfdaaba21d46e

Published CVSS scores

5.5Amazon LinuxCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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.

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Technologies

Your stack

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Your stack

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