What’s Vulnerable › Vulnerabilities

CVE-2021-3996

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2022-08-23 · updated 2026-06-17
• Weakness: CWE-552

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.

Affected products

• Fedoraproject Fedora: 35
• util-linux: from 2.34 before 2.37.3 — fixed in 2.37.3

How to fix

Upgrade to a fixed version: util-linux 2.37.3. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/170176/snap-confine-must_mkdir_and_open_with_perms-Race-Condition.html
• http://seclists.org/fulldisclosure/2022/Dec/4
• http://www.openwall.com/lists/oss-security/2022/11/30/2
• https://access.redhat.com/security/cve/CVE-2021-3996
• https://bugzilla.redhat.com/show_bug.cgi?id=2024628
• https://github.com/util-linux/util-linux/commit/166e87368ae88bf31112a30e078cceae637f4cdb
• https://mirrors.edge.kernel.org/pub/linux/utils/util-linux/v2.37/v2.37.3-ReleaseNotes
• https://security.gentoo.org/glsa/202401-08
• https://security.netapp.com/advisory/ntap-20221209-0002/
• https://www.openwall.com/lists/oss-security/2022/01/24/2
• http://packetstormsecurity.com/files/170176/snap-confine-must_mkdir_and_open_with_perms-Race-Condition.html
• http://seclists.org/fulldisclosure/2022/Dec/4

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