CVE-2021-47342

Kernel crash via dangling MMP thread pointer

Published May 21, 2024 · Updated May 23, 2026

Use-after-free in ext4 in Linux 5.10.51 through 5.10.76 and 5.12.18 through 5.12.19 allows local users to crash the kernel during a read-only remount. A race lets kmmpd exit after the remount while sbi->s_mmp_tsk still references its freed task, and ext4_stop_mmpd then accesses that dangling pointer. Exploitation requires privileges to remount an MMP-protected ext4 file system read-only and can interrupt the host through a kernel crash.

CVSS severity7.8
High
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in ext4 in Linux 5.10.51 through 5.10.76 and 5.12.18 through 5.12.19 allows local users to crash the kernel during a read-only remount. A race lets kmmpd exit after the remount while sbi->s_mmp_tsk still references its freed task, and ext4_stop_mmpd then accesses that dangling pointer. Exploitation requires privileges to remount an MMP-protected ext4 file system read-only and can interrupt the host through a kernel crash.

The record

CVE
CVE-2021-47342
Published
May 21, 2024
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. May 21, 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=5.10.51 <5.10.77
  2. Affected versionversion=5.12.18 <5.13
  3. Affected versionversion=5e4f5138bd8522ebe231a137682d3857209a2c07 <b663890d854403e566169f7e90aed5cd6ff64f6b
  4. Affected versionversion=618f003199c6188e01472b03cdbba227f1dc5f24 <61bb4a1c417e5b95d9edb4f887f131de32e419cb
  5. Affected versionversion=cecfdb9cf9a700d1037066173abac0617f6788df
  6. Affected versionversion=eb7b40d9d3785f7a131fb0b1f89bb6efa46c1833 <7ed572cdf11081f8f9e07abd4bea56a3f2c4edbd

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=5.10.51 <5.10.77; version=5.12.18 <5.13; version=5e4f5138bd8522ebe231a137682d3857209a2c07 <b663890d854403e566169f7e90aed5cd6ff64f6b; version=618f003199c6188e01472b03cdbba227f1dc5f24 <61bb4a1c417e5b95d9edb4f887f131de32e419cb; version=cecfdb9cf9a700d1037066173abac0617f6788df; version=eb7b40d9d3785f7a131fb0b1f89bb6efa46c1833 <7ed572cdf11081f8f9e07abd4bea56a3f2c4edbd

Published CVSS scores

7.8UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
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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