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TI-2021-03525 Aliases CVE-2021-20230GHSA-wwrq-59mq-v8w2

Improper certificate validation in stunnel

Priority LOW 35CWE-295Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Spoofing
Confidentiality · integrity · availability
High · None · None
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-295.

Summary

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.

Why it matters now

EPSS 0.01179 67th percentileScored 2026-11-07
Fix Fixed Red Hat: 3 advisories

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
—stunnelstunnel 5.57—No fix listedCNA
  • stunnel Vendor— Affected stunnel 5.57 Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:stunnel:stunnel:*:*:*:*:*:*:*:*before 5.57VulnerableStunnel
  • cpe:2.3:a:stunnel:stunnel:*:*:*:*:*:*:*:* Versions before 5.57 Vulnerable ·Stunnel

Remediation

Red Hat 3 advisories

  • RHSA-2021:0619 Released 2021-02-22 · Red Hat rating Important
    stunnel security update
    • Red Hat Enterprise Linux BaseOS EUS (v. 8.2) stunnel-5.48-6.el8_2
  • RHSA-2021:0620 Released 2021-02-22 · Red Hat rating Important
    stunnel security update
    • Red Hat Enterprise Linux BaseOS EUS (v. 8.1) stunnel-5.48-6.el8_1
  • RHSA-2021:0618 Released 2021-02-22 · Red Hat rating Important
    stunnel security update
    • Red Hat Enterprise Linux BaseOS (v. 8) stunnel-5.56-5.el8_3

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux BaseOS (v. 8)Fixed RHSA-2021:0618
Red Hat Enterprise Linux BaseOS EUS (v. 8.1)Fixed RHSA-2021:0620
Red Hat Enterprise Linux BaseOS EUS (v. 8.2)Fixed RHSA-2021:0619
Not affected: 4 products
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 9

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-20230
  2. 2026-10-03 Alias added: GHSA-wwrq-59mq-v8w2

References

Patch 1

Advisory 2

  • TI-2011-02592 stunnel 4.40 and 4.41 might allow remote attackers to execute arbitrary code or cause a… CVSS 2.0HIGH 9.3
  • TI-2001-00060 Format string vulnerability in stunnel 3.8 and earlier allows attackers to execute… CVSS 2.0HIGH 10.0
  • TI-2002-00002 Format string vulnerability in stunnel before 3.22 when used in client mode for (1) smtp… CVSS 2.0HIGH 7.5
  • TI-2013-01549 stunnel 4.21 through 4.54, when CONNECT protocol negotiation and NTLM authentication are… CVSS 2.0MEDIUM 6.6
  • TI-2008-02320 The OCSP functionality in stunnel before 4.24 does not properly search certificate… CVSS 2.0MEDIUM 6.8
  • TI-2003-00142 OpenSSL does not use RSA blinding by default, which allows local and remote attackers to… CVSS 2.0MEDIUM 5.0
See all 11 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences