CVE-2021-3995Public exploit

Local service interruption via UID-prefix owner check

Published Aug 23, 2022 · Updated Aug 3, 2024

Improper authorization in util-linux before 2.37.3 allows local users to unmount another user's FUSE filesystem through umount. is_fuse_usermount compares only the user_id option's character length against the current UID, so UID 1000 matches owners 1, 10, or 100. The target must be a FUSE mount whose owner's decimal UID prefixes the attacker's UID; unmounting it interrupts dependent applications.

CVSS severity5.5
Medium
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authorization in util-linux before 2.37.3 allows local users to unmount another user's FUSE filesystem through umount. is_fuse_usermount compares only the user_id option's character length against the current UID, so UID 1000 matches owners 1, 10, or 100. The target must be a FUSE mount whose owner's decimal UID prefixes the attacker's UID; unmounting it interrupts dependent applications.

The record

CVE
CVE-2021-3995
Published
Aug 23, 2022
Updated
Aug 3, 2024
Vendor
util-linux
Product
util-linux
Classifications
T1489
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 23, 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=Fixed in util-linux v2.37.3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

util-linux · util-linuxversion=Fixed in util-linux v2.37.3

Published CVSS scores

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 exploitPublished

Weakness, pattern, technique

T1489Service Stop

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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