CVE-2021-3996Public exploit

Local service interruption via mountpoint suffix stripping

Published Aug 23, 2022 · Updated Oct 15, 2024

Logic error in libmount in util-linux 2.34 through 2.37.2 allows local users to unmount other users' filesystems through FUSE handling. mnt_parse_mountinfo_line blindly strips a literal " (deleted)" suffix from mountpoint paths, causing a crafted nested FUSE mount to resolve as its parent mountpoint. A logged-in unprivileged user needs a target filesystem that is world-writable or mounted beneath a world-writable directory; 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
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Logic error in libmount in util-linux 2.34 through 2.37.2 allows local users to unmount other users' filesystems through FUSE handling. mnt_parse_mountinfo_line blindly strips a literal " (deleted)" suffix from mountpoint paths, causing a crafted nested FUSE mount to resolve as its parent mountpoint. A logged-in unprivileged user needs a target filesystem that is world-writable or mounted beneath a world-writable directory; unmounting it interrupts dependent applications.

The record

CVE
CVE-2021-3996
Published
Aug 23, 2022
Updated
Oct 15, 2024
Vendor
util-linux
Product
util-linux
Classifications
CWE-552, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 23, 2022CVE publishedPublication date reported by the CVE source.
  2. Oct 15, 2024Record 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=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

5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5Red HatCVSS: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-552Files or Directories Accessible to External Parties
T1499.004Application 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