CVE-2021-3996

Name: CVE-2021-3996
Creator: NVD / NIST
Published: 2022-08-23T20:15:08.56+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.5/10EPSS 0.63%

Last modified Jun 17, 2026

CVE-2021-3996 is a medium-severity vulnerability rated 5.5/10 on the CVSS scale. A logic error was found in the libmount library of util-linux in the function that allows an unprivileged user to unmount a FUSE filesystem. This flaw allows a local user on a vulnerable system to unmount other users' filesystems that are either world-writable themselves (like /tmp) or mounted in a world-writable directory. EPSS estimates a 0.63% chance of exploitation in the next 30 days.

Description

A logic error was found in the libmount library of util-linux in the function that allows an unprivileged user to unmount a FUSE filesystem. This flaw allows a local user on a vulnerable system to unmount other users' filesystems that are either world-writable themselves (like /tmp) or mounted in a world-writable directory. An attacker may use this flaw to cause a denial of service to applications that use the affected filesystems.

Metrics

CVSS 3.1

5.5/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.63%

45.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Kernel	Util-Linux	>= 2.34, < 2.37.3
Fedoraproject	Fedora	35

References

http://packetstormsecurity.com/files/170176/snap-confine-must_mkdir_and_open_with_perms-Race-Condition.htmlThird Party Advisory
http://seclists.org/fulldisclosure/2022/Dec/4Mailing List, Third Party Advisory
http://www.openwall.com/lists/oss-security/2022/11/30/2Mailing List, Third Party Advisory
https://access.redhat.com/security/cve/CVE-2021-3996Issue Tracking, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2024628Issue Tracking, Patch, Third Party Advisory
https://github.com/util-linux/util-linux/commit/166e87368ae88bf31112a30e078cceae637f4cdbPatch, Third Party Advisory
https://mirrors.edge.kernel.org/pub/linux/utils/util-linux/v2.37/v2.37.3-ReleaseNotesRelease Notes, Vendor Advisory
https://security.gentoo.org/glsa/202401-08
https://security.netapp.com/advisory/ntap-20221209-0002/Broken Link, Third Party Advisory
https://www.openwall.com/lists/oss-security/2022/01/24/2Exploit, Mailing List, Patch, Third Party Advisory
http://packetstormsecurity.com/files/170176/snap-confine-must_mkdir_and_open_with_perms-Race-Condition.htmlThird Party Advisory
http://seclists.org/fulldisclosure/2022/Dec/4Mailing List, Third Party Advisory
http://www.openwall.com/lists/oss-security/2022/11/30/2Mailing List, Third Party Advisory
https://access.redhat.com/security/cve/CVE-2021-3996Issue Tracking, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2024628Issue Tracking, Patch, Third Party Advisory
https://github.com/util-linux/util-linux/commit/166e87368ae88bf31112a30e078cceae637f4cdbPatch, Third Party Advisory
https://mirrors.edge.kernel.org/pub/linux/utils/util-linux/v2.37/v2.37.3-ReleaseNotesRelease Notes, Vendor Advisory
https://security.gentoo.org/glsa/202401-08
https://security.netapp.com/advisory/ntap-20221209-0002/Broken Link, Third Party Advisory
https://www.openwall.com/lists/oss-security/2022/01/24/2Exploit, Mailing List, Patch, Third Party Advisory

Timeline

Published: Aug 23, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-3996?

How severe is CVE-2021-3996?

CVE-2021-3996 has a CVSS score of 5.5/10 (MEDIUM severity). The EPSS model estimates a 0.63% probability of exploitation in the next 30 days.

How do I fix CVE-2021-3996?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-3996?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST