CVE-2021-38203

Local service hang via concurrent chunk allocation

Published Aug 8, 2021 · Updated Aug 4, 2024

Improper locking in Btrfs in the Linux kernel before 5.13.4 allows local users to hang filesystem operations through concurrent chunk allocation. With system space low, one allocator waits for an unfinished system block group while the allocating task needs another chunk but cannot proceed because the waiting task set the allocation flag. A local user must drive concurrent allocations on a space-constrained Btrfs filesystem; the deadlock interrupts filesystem service without reported data exposure or modification.

CVSS severity5.5
Medium
EPSS probability0.36%
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 Btrfs in the Linux kernel before 5.13.4 allows local users to hang filesystem operations through concurrent chunk allocation. With system space low, one allocator waits for an unfinished system block group while the allocating task needs another chunk but cannot proceed because the waiting task set the allocation flag. A local user must drive concurrent allocations on a space-constrained Btrfs filesystem; the deadlock interrupts filesystem service without reported data exposure or modification.

The record

CVE
CVE-2021-38203
Published
Aug 8, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-667, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

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

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
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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