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Fencer Vulns
medium 5.9

CVE-2021-20251 json

A flaw was found in samba.

published 2023-03-06 3 y ago modified 2026-06-17 4 mo ago also EUVD-2021-7689

cvss
5.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

A flaw was found in samba. A race condition in the password lockout code may lead to the risk of brute force attacks being successful if special conditions are met.

Patch / fix

  • samba samba 4.16.8, 4.17.4
  • samba Debian 14, Debian 13, Debian 12 2:4.17.2+dfsg-3

debian advisories DEBIAN-CVE-2021-20251

  • samba Enterprise Storage 7 4.13.13+git.616.557146479a-150200.3.21.1
  • samba SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLE High Performance Computing 15 SP1-LTSS +3 more 4.9.5+git.552.fec1a5e57a-150100.3.73.1
  • samba SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 +1 more 4.15.13+git.534.0d9f8ece26-3.77.1
  • samba SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLE High Performance Computing 15 SP2-LTSS +3 more 4.11.14+git.384.5dc2c21dce-150200.4.44.1
  • samba SLES for SAP 15 SP3, SLES 15 SP3-LTSS, SLE Real Time 15 SP3 +9 more 4.15.13+git.591.ab36624310c-150300.3.49.1
  • samba SLE Module for Basesystem 15 SP4, SLE Micro 5.3, SLE High Availability Extension 15 SP4 +2 more 4.15.13+git.591.ab36624310c-150400.3.19.1
  • samba SLES for SAP 12 SP4, SLES 12 SP4-LTSS, SLE High Availability Extension 12 SP4 +2 more 4.6.16+git.384.9fec958bed-3.76.1
  • samba SLES 12 SP2-BCL 4.4.2-38.55.1

suse advisories SUSE-SU-2023:0620-1SUSE-SU-2023:0222-1SUSE-SU-2023:0164-1SUSE-SU-2023:0163-1SUSE-SU-2023:0162-1SUSE-SU-2023:0160-1

  • samba openSUSE Tumbleweed 4.17.1+git.270.17afe7cb6b-1.1

opensuse advisories openSUSE-SU-2024:12435-1

  • samba Azure Linux 3.0 4.18.3-1

azure linux advisories AZL-36998

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-20251 updated cvss 5.9

samba: Race condition in the bad password lockout code

  • Red Hat Enterprise Linux 6 samba, samba4, samba4-dc, samba-swat, samba4-libs, samba4-pidl, +17 more Red Hat Enterprise Linux 7 ctdb, samba, samba-dc, ctdb-tests, samba-libs, samba-pidl, +18 more Red Hat Enterprise Linux 8 ctdb, samba, libnetapi, ctdb-tests, samba-libs, samba-pidl, +24 more Red Hat Enterprise Linux 9 ctdb, samba, libldb, ldb-tools, libnetapi, samba-libs, +27 more Red Hat Storage 3 ctdb, samba, samba-dc, ctdb-tests, samba-libs, samba-pidl, +21 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
20 mo ago

Exploit prediction

0.76% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.samba.org https://bugzilla.samba.org/show_bug.cgi?id=14611 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

  • n/a samba

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.