CVE-2021-47638

Local privilege escalation via UBIFS whiteout double free

Published Feb 26, 2025 · Updated Aug 5, 2026

Double free in Linux kernel UBIFS allows local users to crash the host or execute kernel code through a whiteout rename on a writable volume. When ubifs_budget_space fails in rename_whiteout, the error path frees whiteout_ui->data before iput reaches ubifs_free_inode and frees the same allocation again. Directory write access on a mounted writable UBIFS volume is sufficient; allocator corruption can panic the kernel or permit control-flow hijacking.

CVSS severity8.4
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in Linux kernel UBIFS allows local users to crash the host or execute kernel code through a whiteout rename on a writable volume. When ubifs_budget_space fails in rename_whiteout, the error path frees whiteout_ui->data before iput reaches ubifs_free_inode and frees the same allocation again. Directory write access on a mounted writable UBIFS volume is sufficient; allocator corruption can panic the kernel or permit control-flow hijacking.

The record

CVE
CVE-2021-47638
Published
Feb 26, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-415, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 26, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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=4.9
  2. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <14276d38c89a170363e90b6ac0a53c3cf61b87fc
  3. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <2ad07009c459e56ebdcc089d850d664660fdb742
  4. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <2b3236ecf96db7af5836e1366ce39ace8ce832fa
  5. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <40a8f0d5e7b3999f096570edab71c345da812e3e
  6. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <6d7a158a7363c1f6604aa47ae1a280a5c65123dd
  7. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <8b3c7be16f3f4dfd6e15ac651484e59d3fa36274
  8. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <a90e2dbe66d2647ff95a0442ad2e86482d977fd8
  9. Affected versionversion=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <b9a937f096e608b3368c1abc920d4d640ba2c94f

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.9; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <14276d38c89a170363e90b6ac0a53c3cf61b87fc; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <2ad07009c459e56ebdcc089d850d664660fdb742; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <2b3236ecf96db7af5836e1366ce39ace8ce832fa; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <40a8f0d5e7b3999f096570edab71c345da812e3e; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <6d7a158a7363c1f6604aa47ae1a280a5c65123dd; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <8b3c7be16f3f4dfd6e15ac651484e59d3fa36274; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <a90e2dbe66d2647ff95a0442ad2e86482d977fd8; version=9e0a1fff8db56eaaebb74b4a3ef65f86811c4798 <b9a937f096e608b3368c1abc920d4d640ba2c94f

Published CVSS scores

5.5CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
8.4LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5CanonicalCVSS: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-415Double Free
T1068Exploitation for Privilege Escalation

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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