CVE-2021-3847Public exploit

Local root escalation via capability-preserving copy-up

Published Apr 1, 2022 · Updated Aug 3, 2024

Improper permission preservation in Linux Kernel OverlayFS through 5.17 allows local users to gain root via a crafted overlay mount. During copy_up, OverlayFS copies the lower file's security.capability extended attribute into the upper layer with the mounting task's credentials, even when the lower filesystem is mounted nosuid. The path requires a writable overlay whose nosuid lower layer contains a capability-bearing executable; the upstream maintainer describes this as intended administrator-controlled behavior.

CVSS severity7.8
High
EPSS probability0.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper permission preservation in Linux Kernel OverlayFS through 5.17 allows local users to gain root via a crafted overlay mount. During copy_up, OverlayFS copies the lower file's security.capability extended attribute into the upper layer with the mounting task's credentials, even when the lower filesystem is mounted nosuid. The path requires a writable overlay whose nosuid lower layer contains a capability-bearing executable; the upstream maintainer describes this as intended administrator-controlled behavior.

The record

CVE
CVE-2021-3847
Published
Apr 1, 2022
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-281, T1068
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Apr 1, 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=all versions up to, including, kernel 5.17

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

The Linux Kernel Organization · Linux Kernelversion=all versions up to, including, kernel 5.17

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.

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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-281Improper Preservation of Permissions
T1068Exploitation for Privilege Escalation

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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