Security readout for executives and security teams
Plain-English summary
CVE-2021-3996 is a local denial-of-service issue in util-linux libmount. A logged-in unprivileged user may be able to unmount another user's FUSE filesystem when it is world-writable or mounted under a world-writable directory such as /tmp, disrupting applications that depend on it.
Executive priority
Treat this as a moderate operational risk, not a remote compromise emergency. Prioritize patching on shared Linux systems and systems where application availability depends on FUSE mounts in writable shared paths.
Technical view
The flaw is a libmount logic error in the path that permits unprivileged FUSE unmounts. The CVSS vector is local, low complexity, low privileges, no user interaction, and high availability impact. The source bundle says util-linux v2.37.3 contains the fix.
Likely exposure
Exposure is mainly Linux systems with vulnerable util-linux/libmount versions where local users exist and FUSE filesystems are mounted in world-writable locations. Single-user systems or systems without such FUSE mount patterns are less likely to be practically exposed, based on the supplied description.
Exploitation context
The source bundle does not show CISA KEV listing or confirmed active exploitation. Exploitation requires local access, so the main concern is shared servers, developer workstations, or multi-user environments where a local account can disrupt another user's mounted filesystem.
Researcher notes
Do not overstate scope: the supplied evidence supports local denial of service only. Several references in the bundle concern CVE-2022-3328 and should not be used to infer CVE-2021-3996 exploitability or affected software.
Mitigation direction
- Update util-linux to v2.37.3 or a vendor package containing the backported fix.
- Check Linux distribution advisories for exact fixed package versions.
- Avoid placing FUSE mounts in world-writable directories where operationally feasible.
- Limit unnecessary local shell access on shared systems.
- Monitor for unexpected FUSE unmounts affecting critical applications.
Validation and detection
- Inventory util-linux versions on Linux hosts.
- Confirm vendor package metadata includes the CVE-2021-3996 fix.
- Identify FUSE filesystems mounted in world-writable paths.
- Prioritize shared systems with untrusted or semi-trusted local users.
- Review application incidents for unexpected filesystem unmounts.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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CWE-552: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-3996 mapping review
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Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://mirrors.edge.kernel.org/pub/linux/utils/util-linux/v2.37/v2.37.3-ReleaseNotesCVE reference
- https://github.com/util-linux/util-linux/commit/166e87368ae88bf31112a30e078cceae637f4cdbCVE reference
- https://www.openwall.com/lists/oss-security/2022/01/24/2CVE reference
- https://bugzilla.redhat.com/show_bug.cgi?id=2024628CVE reference
- https://access.redhat.com/security/cve/CVE-2021-3996CVE reference
- https://security.netapp.com/advisory/ntap-20221209-0002/CVE reference
- GLSA-202401-08CVE reference · vendor-advisory
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Files or Directories Accessible to External Parties
Files or Directories Accessible to External Parties represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.