CVE-2021-47637Public exploit

Filesystem hang via UBIFS inode-lock inversion

Published Feb 26, 2025 · Updated May 11, 2026

Improper locking in Linux kernel UBIFS 4.9 through 5.17.1 allows local users to hang filesystem operations via a rename race. ubifs_rename locks four inodes before budgeting whiteout space, then waits for writeback while ubifs_write_inode waits on the same ui_mutex. Exploitation requires a UBIFS mount, RENAME_WHITEOUT, concurrent writeback, and depleted free space; affected tasks remain blocked.

CVSS severity5.5
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper locking in Linux kernel UBIFS 4.9 through 5.17.1 allows local users to hang filesystem operations via a rename race. ubifs_rename locks four inodes before budgeting whiteout space, then waits for writeback while ubifs_write_inode waits on the same ui_mutex. Exploitation requires a UBIFS mount, RENAME_WHITEOUT, concurrent writeback, and depleted free space; affected tasks remain blocked.

The record

CVE
CVE-2021-47637
Published
Feb 26, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 26, 2025CVE 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.9
  2. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <37bdf1ad592555ecda1d55b89f6e393e4c0589d1
  3. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <70e9090acc32348cedc5def0cd6d5c126efc97b9
  4. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <83e42a78428fc354f5e2049935b84c8d8d29b787
  5. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <8b278c8dcfb565cb65eceb62a38cbf7a7c326db5
  6. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <9dddc8211430fb851ddf0b168e3a00c6f66cc185
  7. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <afd427048047e8efdedab30e8888044e2be5aa9c
  8. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <c58af8564a7b08757173009030b74baf4b2b762b

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.9; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <37bdf1ad592555ecda1d55b89f6e393e4c0589d1; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <70e9090acc32348cedc5def0cd6d5c126efc97b9; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <83e42a78428fc354f5e2049935b84c8d8d29b787; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <8b278c8dcfb565cb65eceb62a38cbf7a7c326db5; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <9dddc8211430fb851ddf0b168e3a00c6f66cc185; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <afd427048047e8efdedab30e8888044e2be5aa9c; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <c58af8564a7b08757173009030b74baf4b2b762b

Published CVSS scores

5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5CISA-ADPCVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-667Improper Locking
T1499.004Endpoint Denial of Service Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo