CVE-2021-4149Public exploit

Local kernel deadlock via locked buffer release

Published Mar 23, 2022 · Updated Aug 3, 2024

Improper locking in Linux kernel 5.4 through 5.15-rc5 allows local users to hang or crash the system through Btrfs error handling. In btrfs_alloc_tree_block(), failure after btrfs_init_new_buffer() frees the newly allocated extent buffer without first releasing its tree lock. Local access to a Btrfs filesystem and a later allocation or delayed-reference failure are required; the bounded consequence is a kernel deadlock or crash.

CVSS severity5.5
Medium
EPSS probability0.40%
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 5.4 through 5.15-rc5 allows local users to hang or crash the system through Btrfs error handling. In btrfs_alloc_tree_block(), failure after btrfs_init_new_buffer() frees the newly allocated extent buffer without first releasing its tree lock. Local access to a Btrfs filesystem and a later allocation or delayed-reference failure are required; the bounded consequence is a kernel deadlock or crash.

The record

CVE
CVE-2021-4149
Published
Mar 23, 2022
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-667, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 23, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=kernel 5.15 rc6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=kernel 5.15 rc6

Published CVSS scores

2.1NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.7SUSECVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5OracleCVSS:3.0/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 exploitPublished

Weakness, pattern, technique

CWE-667Improper Locking
T1499.004Application or System Exploitation

Public exploit references

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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