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Fencer Vulns
medium 6.8

CVE-2021-20254 json

A flaw was found in samba.

published 2021-05-05 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-7692

cvss
6.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 76%
public exploits
0
none known

Summary

A flaw was found in samba. The Samba smbd file server must map Windows group identities (SIDs) into unix group ids (gids). The code that performs this had a flaw that could allow it to read data beyond the end of the array in the case where a negative cache entry had been added to the mapping cache. This could cause the calling code to return those values into the process token that stores the group membership for a user. The highest threat from this vulnerability is to data confidentiality and integrity.

Patch / fix

  • samba samba 4.12.15, 4.13.8, 4.14.4
  • samba Debian 14, Debian 13, Debian 12 2:4.13.5+dfsg-2

debian advisories DEBIAN-CVE-2021-20254

  • samba Ubuntu 16.04 LTS 2:4.3.11+dfsg-0ubuntu0.16.04.34
  • samba Ubuntu 18.04 LTS 2:4.7.6+dfsg~ubuntu-0ubuntu2.23
  • samba Ubuntu 20.04 LTS 2:4.11.6+dfsg-0ubuntu1.8
  • samba Ubuntu Pro 14.04 LTS 2:4.3.11+dfsg-0ubuntu0.14.04.20+esm11

ubuntu advisories UBUNTU-CVE-2021-20254

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • samba RHEL 8 4.13.3-5.el8_4
  • ctdb RHEL 8 4.13.3-5.el8_4
  • ctdb-tests RHEL 8 4.13.3-5.el8_4
  • samba-libs RHEL 8 4.13.3-5.el8_4
  • samba-pidl RHEL 8 4.13.3-5.el8_4
  • samba-test RHEL 8 4.13.3-5.el8_4
  • libwbclient RHEL 8 4.13.3-5.el8_4
  • libsmbclient RHEL 8 4.13.3-5.el8_4

red hat advisories RHSA-2021:4866RHSA-2021:4058RHSA-2021:3988RHSA-2021:3723RHSA-2021:3724RHSA-2021:2313

  • samba Enterprise Storage 7 4.13.13+git.545.5897c2d94f3-3.12.1
  • ldb Enterprise Storage 7 2.2.2-4.6.1
  • samba SLE Module for Python 2 15 SP3, SLE Module for Basesystem 15 SP3, SLE High Availability Extension 15 SP3 4.13.6+git.211.555d60b24ba-3.7.1
  • samba SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +7 more 4.9.5+git.432.d9b18c4f390-3.50.1
  • samba SLES for SAP 12 SP4, SLES for SAP 12 SP3, SLES 12 SP4-LTSS +9 more 4.6.16+git.282.cfafed5922a-3.61.1
  • samba SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +2 more 4.7.11+git.316.432f0218290-4.54.1
  • samba SLE Module for Python 2 15 SP2, SLE Module for Basesystem 15 SP2, SLE High Availability Extension 15 SP2 4.11.14+git.247.8c858f7ee14-4.19.1
  • samba SLES 12 SP2-BCL 4.2.4-28.39.1

suse advisories SUSE-SU-2022:0361-1SUSE-SU-2021:3187-1SUSE-SU-2021:1498-1SUSE-SU-2021:1492-1SUSE-SU-2021:1445-1SUSE-SU-2021:1444-1

  • samba openSUSE Tumbleweed 4.14.6+git.182.2205d5224e3-1.1
  • samba openSUSE Leap 15.3 4.13.6+git.211.555d60b24ba-3.7.1
  • samba openSUSE Leap 15.2 4.11.14+git.247.8c858f7ee14-lp152.3.19.1

opensuse advisories openSUSE-SU-2024:11365-1openSUSE-SU-2021:3187-1openSUSE-SU-2021:0636-1

  • samba Rocky Linux 8 4.13.3-5.el8_4

rocky linux advisories RLSA-2021:4058

  • samba Alpine 3.12 4.12.15-r0
  • samba Alpine 3.13 4.13.8-r0
  • samba Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 4.14.4-r0

alpine advisories ALPINE-CVE-2021-20254

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • samba Azure Linux 3.0 4.18.3-1

azure linux advisories AZL-36999

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

  • samba Arch Linux 4.14.4-1

arch linux advisories AVG-1893

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-2021-20254 updated cvss 6.8

samba: Negative idmap cache entries can cause incorrect group entries in the Samba file server process token

  • Red Hat Enterprise Linux 6 samba, samba4, samba4-dc, samba-swat, samba4-libs, samba4-pidl, +17 more
    affected: no fix planned “Out of support scope”
  • Red Hat CodeReady Linux Builder (v. 8) ctdb 4.13.3-5.el8_4, samba 4.13.3-5.el8_4, ctdb-tests 4.13.3-5.el8_4, samba-libs 4.13.3-5.el8_4, samba-pidl 4.13.3-5.el8_4, samba-test 4.13.3-5.el8_4, +16 more
    fixed: vendor fix RHSA-2021:4058
  • Red Hat CodeReady Linux Builder EUS (v. 8.2) ctdb 4.11.2-15.el8_2, samba 4.11.2-15.el8_2, ctdb-tests 4.11.2-15.el8_2, samba-libs 4.11.2-15.el8_2, samba-pidl 4.11.2-15.el8_2, samba-test 4.11.2-15.el8_2, +15 more
    fixed: vendor fix RHSA-2021:4866
  • Red Hat Enterprise Linux BaseOS (v. 8) ctdb 4.13.3-5.el8_4, samba 4.13.3-5.el8_4, ctdb-tests 4.13.3-5.el8_4, samba-libs 4.13.3-5.el8_4, samba-pidl 4.13.3-5.el8_4, samba-test 4.13.3-5.el8_4, +16 more
    fixed: vendor fix RHSA-2021:4058
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.2) ctdb 4.11.2-15.el8_2, samba 4.11.2-15.el8_2, ctdb-tests 4.11.2-15.el8_2, samba-libs 4.11.2-15.el8_2, samba-pidl 4.11.2-15.el8_2, samba-test 4.11.2-15.el8_2, +15 more
    fixed: vendor fix RHSA-2021:4866
  • Red Hat Enterprise Linux Client (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more Red Hat Enterprise Linux Client Optional (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more Red Hat Enterprise Linux ComputeNode Optional (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more Red Hat Enterprise Linux Server (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more
    fixed: vendor fix RHSA-2021:2313
  • Red Hat Enterprise Linux Server AUS (v. 7.7) samba 4.9.1-11.el7_7, samba-dc 4.9.1-11.el7_7, samba-libs 4.9.1-11.el7_7, samba-pidl 4.9.1-11.el7_7, samba-test 4.9.1-11.el7_7, libwbclient 4.9.1-11.el7_7, +16 more Red Hat Enterprise Linux Server E4S (v. 7.7) samba 4.9.1-11.el7_7, samba-dc 4.9.1-11.el7_7, samba-libs 4.9.1-11.el7_7, samba-pidl 4.9.1-11.el7_7, samba-test 4.9.1-11.el7_7, libwbclient 4.9.1-11.el7_7, +15 more
    fixed: vendor fix RHSA-2021:3988
  • Red Hat Enterprise Linux Server Optional (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more
    fixed: vendor fix RHSA-2021:2313
show 7 more
  • Red Hat Enterprise Linux Server Optional AUS (v. 7.7) samba 4.9.1-11.el7_7, samba-dc 4.9.1-11.el7_7, samba-libs 4.9.1-11.el7_7, samba-pidl 4.9.1-11.el7_7, samba-test 4.9.1-11.el7_7, libwbclient 4.9.1-11.el7_7, +16 more Red Hat Enterprise Linux Server Optional E4S (v. 7.7) samba 4.9.1-11.el7_7, samba-dc 4.9.1-11.el7_7, samba-libs 4.9.1-11.el7_7, samba-pidl 4.9.1-11.el7_7, samba-test 4.9.1-11.el7_7, libwbclient 4.9.1-11.el7_7, +15 more Red Hat Enterprise Linux Server Optional TUS (v. 7.7) samba 4.9.1-11.el7_7, samba-dc 4.9.1-11.el7_7, samba-libs 4.9.1-11.el7_7, samba-pidl 4.9.1-11.el7_7, samba-test 4.9.1-11.el7_7, libwbclient 4.9.1-11.el7_7, +16 more
    fixed: vendor fix RHSA-2021:3988
  • Red Hat Enterprise Linux Server Resilient Storage (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more
    fixed: vendor fix RHSA-2021:2313
  • Red Hat Enterprise Linux Server TUS (v. 7.7) samba 4.9.1-11.el7_7, samba-dc 4.9.1-11.el7_7, samba-libs 4.9.1-11.el7_7, samba-pidl 4.9.1-11.el7_7, samba-test 4.9.1-11.el7_7, libwbclient 4.9.1-11.el7_7, +16 more
    fixed: vendor fix RHSA-2021:3988
  • Red Hat Enterprise Linux Workstation (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more Red Hat Enterprise Linux Workstation Optional (v. 7) ctdb 4.10.16-15.el7_9, samba 4.10.16-15.el7_9, samba-dc 4.10.16-15.el7_9, ctdb-tests 4.10.16-15.el7_9, samba-libs 4.10.16-15.el7_9, samba-pidl 4.10.16-15.el7_9, +18 more
    fixed: vendor fix RHSA-2021:2313
  • Red Hat Gluster 3.5 Samba on RHEL-7 ctdb 4.11.6-112.el7rhgs, samba 4.11.6-112.el7rhgs, samba-libs 4.11.6-112.el7rhgs, samba-pidl 4.11.6-112.el7rhgs, libwbclient 4.11.6-112.el7rhgs, libsmbclient 4.11.6-112.el7rhgs, +12 more
    fixed: vendor fix RHSA-2021:3723
  • Red Hat Gluster 3.5 Samba on RHEL-8 ctdb 4.14.5-201.el8rhgs, samba 4.14.5-201.el8rhgs, samba-libs 4.14.5-201.el8rhgs, samba-pidl 4.14.5-201.el8rhgs, libwbclient 4.14.5-201.el8rhgs, libsmbclient 4.14.5-201.el8rhgs, +12 more
    fixed: vendor fix RHSA-2021:3724
  • Red Hat Enterprise Linux 9 ctdb, samba, libnetapi, samba-libs, samba-pidl, samba-test, +23 more Red Hat Gluster 3.5 Samba on RHEL-8 libtalloc 2.3.2-5.el8rhgs, python3-talloc 2.3.2-5.el8rhgs
    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

Exploit prediction

1.62% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 4.9 AV:N/AC:M/Au:S/C:P/I:P/A:N

Affected products

  • n/a samba

Classification

Weakness

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.