CVE-2021-20230

mediumpriority · track · 30EPSS 0.012 · 68 %ileDEEURUUS
grimoire priorityP3 · Track
Exploitable?
—
no known exploitation
Likely / severe?
1.18% (68th) EPSS
CVSS 5 · medium
Is it mine?
97 products
Check your exposure
Who says so?
5 sources
cnnvd · enisa_euvd · fstec_bdu · cert_bund

EPSS · scored 2026-10-27

A flaw was found in stunnel before 5.57, where it improperly validates client certificates when it is configured to use both redirect and verifyChain options. This flaw allows an attacker with a certificate signed by a Certificate Authority, which is not the one accepted by the stunnel server, to access the tunneled service instead of being redirected to the address specified in the redirect option. The highest threat from this vulnerability is to confidentiality.

01

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

  • Fixedstunnel-0:5.56-5.el8_3.aarch64 as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-0:5.56-5.el8_3.ppc64le as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-0:5.56-5.el8_3.s390x as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-0:5.56-5.el8_3.src as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-0:5.56-5.el8_3.x86_64 as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debuginfo-0:5.56-5.el8_3.aarch64 as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debuginfo-0:5.56-5.el8_3.ppc64le as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debuginfo-0:5.56-5.el8_3.s390x as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debuginfo-0:5.56-5.el8_3.x86_64 as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debugsource-0:5.56-5.el8_3.aarch64 as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debugsource-0:5.56-5.el8_3.ppc64le as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debugsource-0:5.56-5.el8_3.s390x as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-debugsource-0:5.56-5.el8_3.x86_64 as a component of Red Hat Enterprise Linux BaseOS (v. 8)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0618
  • Fixedstunnel-0:5.48-6.el8_2.aarch64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-0:5.48-6.el8_2.ppc64le as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-0:5.48-6.el8_2.s390x as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-0:5.48-6.el8_2.src as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-0:5.48-6.el8_2.x86_64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debuginfo-0:5.48-6.el8_2.aarch64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debuginfo-0:5.48-6.el8_2.ppc64le as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debuginfo-0:5.48-6.el8_2.s390x as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debuginfo-0:5.48-6.el8_2.x86_64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debugsource-0:5.48-6.el8_2.aarch64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debugsource-0:5.48-6.el8_2.ppc64le as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debugsource-0:5.48-6.el8_2.s390x as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-debugsource-0:5.48-6.el8_2.x86_64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.2)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0619
  • Fixedstunnel-0:5.48-6.el8_1.aarch64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-0:5.48-6.el8_1.ppc64le as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-0:5.48-6.el8_1.s390x as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-0:5.48-6.el8_1.src as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-0:5.48-6.el8_1.x86_64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debuginfo-0:5.48-6.el8_1.aarch64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debuginfo-0:5.48-6.el8_1.ppc64le as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debuginfo-0:5.48-6.el8_1.s390x as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debuginfo-0:5.48-6.el8_1.x86_64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debugsource-0:5.48-6.el8_1.aarch64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debugsource-0:5.48-6.el8_1.ppc64le as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debugsource-0:5.48-6.el8_1.s390x as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
  • Fixedstunnel-debugsource-0:5.48-6.el8_1.x86_64 as a component of Red Hat Enterprise Linux BaseOS EUS (v. 8.1)redhat_csaf

    For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258

    https://access.redhat.com/errata/RHSA-2021:0620
02

cvss

Technical severity, 0–10. One row per scoring source.

7.5
010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5–7.5

v2.05mediumAV:N/AC:L/Au:N/C:P/I:N/A:Nprimary · NVD / NIST USexploitability 10 · impact 2.9
v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Nprimary · NVD / NIST USexploitability 3.9 · impact 3.6
v3.17.5highAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Nsecondary · FSTEC (BDU) RU
v3.16.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:Usecondary · CVSS-BT (t0sche)
v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Nsecondary · Red Hat Product Security US
03

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-295USCWE-295USCWE-295US
04

affected products (97)

Products and version ranges known to be affected.

showing 20 of 97
05

advisories (4)

Vendor and ecosystem advisories describing this.

  • RHSA-2021:0618Red Hat Security Advisory: stunnel security update2021-02-22csaf · redhat_csafUS

    An update for stunnel is now available for Red Hat Enterprise Linux 8. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

  • RHSA-2021:0619Red Hat Security Advisory: stunnel security update2021-02-22csaf · redhat_csafUS

    An update for stunnel is now available for Red Hat Enterprise Linux 8.2 Extended Update Support. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

  • RHSA-2021:0620Red Hat Security Advisory: stunnel security update2021-02-22csaf · redhat_csafUS

    An update for stunnel is now available for Red Hat Enterprise Linux 8.1 Extended Update Support. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

  • WID-SEC-W-2024-1674Red Hat Enterprise Linux: Schwachstelle ermöglicht Umgehen von SicherheitsvorkehrungenDeutsch2021-02-21csaf · cert_bundDE

    Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Red Hat Enterprise Linux ausnutzen, um Sicherheitsvorkehrungen zu umgehen.

06

also known as (4)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

cnnvdenisa_euvdfstec_bducert_bundredhat_csafNVDCVE.orgMITRE
published 2021-02-23modified 2026-06-17
08

references (18)

External citations — patches, advisories, analysis.

scry

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