CVE-2021-46939

System hang via recursive tracing spinlock deadlock

Published Feb 27, 2024 · Updated May 11, 2026

Improper synchronization in Linux kernel tracing allows local users to hang an affected system during suspend or resume. When function-graph tracing recursively reenters ring_buffer_lock_reserve(), trace_clock_global() takes the same spin lock twice instead of avoiding a blocking update of prev_time. The path requires local low-privileged access and function-graph tracing during a power-management transition; the bounded consequence is a system deadlock.

CVSS severity5.5
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

Improper synchronization in Linux kernel tracing allows local users to hang an affected system during suspend or resume. When function-graph tracing recursively reenters ring_buffer_lock_reserve(), trace_clock_global() takes the same spin lock twice instead of avoiding a blocking update of prev_time. The path requires local low-privileged access and function-graph tracing during a power-management transition; the bounded consequence is a system deadlock.

The record

CVE
CVE-2021-46939
Published
Feb 27, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-662, CWE-400
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 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=14131f2f98ac350ee9e73faed916d2238a8b6a0d <1fca00920327be96f3318224f502e4d5460f9545
  2. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <2a1bd74b8186d7938bf004f5603f25b84785f63e
  3. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <6e2418576228eeb12e7ba82edb8f9500623942ff
  4. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b
  5. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <91ca6f6a91f679c8645d7f3307e03ce86ad518c4
  6. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <a33614d52e97fc8077eb0b292189ca7d964cc534
  7. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <aafe104aa9096827a429bc1358f8260ee565b7cc
  8. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <c64da3294a7d59a4bf6874c664c13be892f15f44
  9. Affected versionversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <d43d56dbf452ccecc1ec735cd4b6840118005d7c
  10. Affected versionversion=2.6.30

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=14131f2f98ac350ee9e73faed916d2238a8b6a0d <1fca00920327be96f3318224f502e4d5460f9545; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <2a1bd74b8186d7938bf004f5603f25b84785f63e; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <6e2418576228eeb12e7ba82edb8f9500623942ff; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <91ca6f6a91f679c8645d7f3307e03ce86ad518c4; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <a33614d52e97fc8077eb0b292189ca7d964cc534; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <aafe104aa9096827a429bc1358f8260ee565b7cc; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <c64da3294a7d59a4bf6874c664c13be892f15f44; version=14131f2f98ac350ee9e73faed916d2238a8b6a0d <d43d56dbf452ccecc1ec735cd4b6840118005d7c; version=2.6.30

Published CVSS scores

5.5CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5NIST NVDCVSS: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 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-662Improper Synchronization
CWE-400Uncontrolled Resource Consumption

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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