CVE-2021-3995

Exp

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 an unprivileged local attacker to unmount FUSE filesystems that belong to certain other users who have a UID that is a prefix of the UID of the attacker in its string form. An attacker may use this flaw to cause a denial of service to applications that use the affected filesystems.

Published: 2022-08-23 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3995 is rated Exploit Available (53.3/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.63%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-3995

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-3995

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.20% 0.63% +0.43%
2 2026-03-08 0.26% 0.20% -0.06%
3 2025-12-04 — 0.26% —

Full EPSS history (13 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3995

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]

Weakness enumeration for CVE-2021-3995

OS Trackers for CVE-2021-3995

vendor priority summary link
alpine — CVE-2021-3995: 1 source package rows (util-linux); 13 state rows across 8 repos (3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 5. https://security.alpinelinux.org/vuln/CVE-2021-3995
debian not yet assigned CVE-2021-3995 not yet assigned priority: Debian including 1 source packages (util-linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3995
gentoo normal CVE-2021-3995: 1 GLSA(s) (202401-08), 1 atom(s) (sys-apps/util-linux); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-3995
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3995
suse medium CVE-2021-3995 severity moderate: SUSE including 825 source package names (0.21.0.3.2.10:libblkid1-2.36.2-150300.4.14.3, 0.21.0.3.2.10:libeconf0-0.4.4+git20220104.962774f-150300.3.6.2, …), 1734 product×package rows across 137 product lines (Container bci/bci-init, Container bci/dotnet-aspnet, … (137 product lines)): Fixed 1126, Known Not Affected 424, Known Affected 184. https://www.suse.com/security/cve/CVE-2021-3995/
ubuntu medium CVE-2021-3995 medium priority: Ubuntu including 1 source packages (util-linux), 7 status rows across 7 suites (bionic, focal, impish, jammy, trusty, upstream, xenial): released 4, not-affected 3. https://ubuntu.com/security/CVE-2021-3995

Affected software / configurations for CVE-2021-3995

Vendor Product Version Raw CPE
kernel util-linux >= 2.34, < 2.37.3 cpe:2.3:a:kernel:util-linux:*:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*

References for CVE-2021-3995

URL Tags
http://packetstormsecurity.com/files/170176/snap-confine-must_mkdir_and_open_with_perms-Race-Condition.html Third Party Advisory VDB Entry
http://seclists.org/fulldisclosure/2022/Dec/4 Mailing List Third Party Advisory
http://www.openwall.com/lists/oss-security/2022/11/30/2 Mailing List Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2024631https://access.redhat.com/security/cve/CVE-2021-3995 Broken Link Issue Tracking
https://github.com/util-linux/util-linux/commit/57202f5713afa2af20ffbb6ab5331481d0396f8d Patch Third Party Advisory
https://mirrors.edge.kernel.org/pub/linux/utils/util-linux/v2.37/v2.37.3-ReleaseNotes Release Notes Vendor Advisory
https://security.gentoo.org/glsa/202401-08
https://security.netapp.com/advisory/ntap-20221209-0002/ Third Party Advisory
https://www.openwall.com/lists/oss-security/2022/01/24/2 Exploit Mailing List Patch Third Party Advisory
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