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Debian LinuxOperating system · Debian

CVE-2021-20316

MEDIUM · 6.8 CVSS v3.1 Published 2022-08-23
Fix available
A fix is available. Upgrade to 4.15.0 or later.
See remediation →
74/100
Remediation priority · Elevated
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A flaw was found in the way Samba handled file/directory metadata. This flaw allows an authenticated attacker with permissions to read or modify share metadata, to perform this operation outside of the share.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

This is an authorization bypass vulnerability in Samba's file/directory metadata handling. An authenticated attacker with permissions to read or modify share metadata can perform operations outside the intended share boundaries, potentially accessing or modifying files on the host filesystem outside the allocated share.

MitigationUpdate Samba to the patched version (4.13.17+, 4.14.12+, 4.15.5+ or later). Review share configurations and ensure proper access controls are in place to limit metadata operations to within share boundaries.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Debian LinuxOperating system
Affected:= 10.0= 11.0
Virtualization HostApplication
Affected:= 4.0
Enterprise LinuxOperating system
Affected:= 8.0
Enterprise Linux AusOperating system
Affected:= 8.6
Enterprise Linux EusOperating system
Affected:= 8.6
Enterprise Linux TusOperating system
Affected:= 8.6
SambaApplication
Affected:< 4.15.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Samba version
    Run 'smbd --version' or 'samba --version', or check the package manager output (dpkg -l | grep samba or rpm -qa | grep samba)
    Affected if The installed version is below 4.15.0 (including any 4.13.x before 4.13.17, any 4.14.x before 4.14.12, or any 4.15.x before 4.15.5)
  2. Verify Samba service is running
    Run 'systemctl status smbd' or 'systemctl status samba' depending on your distribution
    Affected if The Samba daemon is active and serving shares
  3. Identify configured shares
    Review /etc/samba/smb.conf and run 'smbclient -L localhost -U username' with valid credentials to list accessible shares
    Affected if Samba shares are configured and accessible to authenticated users
  4. Check for metadata-modifying operations
    Review share configurations in /etc/samba/smb.conf for any custom vfs objects or extended attributes settings, and audit logs in /var/log/samba/ for unusual metadata operations
    Affected if Users with read or modify permissions on share metadata exist and can trigger the flawed code path

If Samba version is below 4.15.0 and the service is running with accessible shares, the environment is likely affected by this authorization bypass in metadata handling.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.15.0 or later
Fixed in 4.15.0
Interim mitigation

Update Samba to the patched version (4.13.17+, 4.14.12+, 4.15.5+ or later). Review share configurations and ensure proper access controls are in place to limit metadata operations to within share boundaries.

Recommended fix High confidence

Samba 4.15.0 or later (or vendor-provided security update containing this fix)

  1. Verify current Samba version with: smbd --version
  2. For Debian 10/11: Check for and apply security updates via: apt update && apt install samba
  3. For RHEL 8.x / CentOS: Check for and apply errata via: yum update samba
  4. For Enterprise Linux variants (Eus, Aus, Tus): Apply via yum update using specific repository
  5. After updating, verify new version is 4.15.0 or later with: smbd --version
  6. Restart Samba services: systemctl restart smbd nmbd
Caveat Review release notes for 4.15.0 for any configuration or feature changes before deploying in production

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-20316 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data