CVE-2021-46987

Filesystem hang via recursive Btrfs range locking

Published Feb 28, 2024 · Updated May 23, 2026

Improper locking in Linux kernel Btrfs allows local users to hang filesystem operations by cloning inline extents with qgroups enabled. During the exceptional inline-data copy path, qgroup metadata reservation can flush delalloc while the destination iotree range is already locked, causing recursive lock acquisition. The condition requires enabled qgroups, an inline extent clone, and metadata pressure; affected tasks enter uninterruptible sleep and filesystem work stalls.

CVSS severity5.5
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper locking in Linux kernel Btrfs allows local users to hang filesystem operations by cloning inline extents with qgroups enabled. During the exceptional inline-data copy path, qgroup metadata reservation can flush delalloc while the destination iotree range is already locked, causing recursive lock acquisition. The condition requires enabled qgroups, an inline extent clone, and metadata pressure; affected tasks enter uninterruptible sleep and filesystem work stalls.

The record

CVE
CVE-2021-46987
Published
Feb 28, 2024
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE 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

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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=36af2de520cca7c37974cc4944b47850f6c460ee
  2. Affected versionversion=5.4.141 <5.5
  3. Affected versionversion=5.9
  4. Affected versionversion=c53e9653605dbf708f5be02902de51831be4b009 <96157707c0420e3d3edfe046f1cc797fee117ade
  5. Affected versionversion=c53e9653605dbf708f5be02902de51831be4b009 <d5347827d0b4b2250cbce6eccaa1c81dc78d8651
  6. Affected versionversion=c53e9653605dbf708f5be02902de51831be4b009 <f8fbbd06fab9b75dcd68d850fe318ac3bc128974
  7. Affected versionversion=c53e9653605dbf708f5be02902de51831be4b009 <f9baa501b4fd6962257853d46ddffbc21f27e344

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=36af2de520cca7c37974cc4944b47850f6c460ee; version=5.4.141 <5.5; version=5.9; version=c53e9653605dbf708f5be02902de51831be4b009 <96157707c0420e3d3edfe046f1cc797fee117ade; version=c53e9653605dbf708f5be02902de51831be4b009 <d5347827d0b4b2250cbce6eccaa1c81dc78d8651; version=c53e9653605dbf708f5be02902de51831be4b009 <f8fbbd06fab9b75dcd68d850fe318ac3bc128974; version=c53e9653605dbf708f5be02902de51831be4b009 <f9baa501b4fd6962257853d46ddffbc21f27e344

Published CVSS scores

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-667Improper Locking
T1499.004Application or System Exploitation

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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