CVE-2021-20254Network attack vector

Unauthorized file access via SID-to-GID out-of-bounds read

Published May 5, 2021 · Updated Aug 3, 2024

Out-of-bounds read in Samba allows remote authenticated users to access files through incorrect group rights in smbd process tokens. SID-to-GID conversion reads beyond an array after a negative idmap cache entry, then inserts stray group IDs into a user process token. A valid SMB account and the cache condition are required; triggering is not reproducible on demand, while observed effects include unauthorized file deletion or a crash.

CVSS severity6.8
Medium
EPSS probability1.62%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Samba allows remote authenticated users to access files through incorrect group rights in smbd process tokens. SID-to-GID conversion reads beyond an array after a negative idmap cache entry, then inserts stray group IDs into a user process token. A valid SMB account and the cache condition are required; triggering is not reproducible on demand, while observed effects include unauthorized file deletion or a crash.

The record

CVE
CVE-2021-20254
Published
May 5, 2021
Updated
Aug 3, 2024
Vendor
PPP Project
Product
Samba
Classifications
CWE-125, T1210
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 5, 2021CVE 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=samba 4.14.1, samba 4.13.6, samba 4.12.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

PPP Project · Sambaversion=samba 4.14.1, samba 4.13.6, samba 4.12.13

Published CVSS scores

6.8Samba TeamCVSS: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-125Out-of-bounds Read
T1210Exploitation of Remote Services

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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