CVE-2021-20316Network attack vector

Out-of-share metadata access via symlink race

Published Aug 23, 2022 · Updated Aug 3, 2024

Symlink race in the Samba file server before 4.15.0 allows remote authenticated users to read or modify metadata outside an exported share. Pathname-based VFS metadata calls follow a client-controlled path while a writable entry is renamed and replaced with a symlink, causing the operation to reach its target. Exploitation requires SMB1 Unix extensions or an overlapping NFS export, permission on the target metadata, and winning a difficult race.

CVSS severity6.8
Medium
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Symlink race in the Samba file server before 4.15.0 allows remote authenticated users to read or modify metadata outside an exported share. Pathname-based VFS metadata calls follow a client-controlled path while a writable entry is renamed and replaced with a symlink, causing the operation to reach its target. Exploitation requires SMB1 Unix extensions or an overlapping NFS export, permission on the target metadata, and winning a difficult race.

The record

CVE
CVE-2021-20316
Published
Aug 23, 2022
Updated
Aug 3, 2024
Vendor
PPP Project
Product
Samba
Classifications
CWE-362, T1222.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 23, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Affects samba file server before v4.15.0, Fixed in samba v4.15.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

PPP Project · Sambaversion=Affects samba file server before v4.15.0, Fixed in samba v4.15.0

Published CVSS scores

6.8NIST NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1222.001File and Directory Permissions Modification: Linux and Mac File and Directory Permissions Modification

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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