CVE-2021-20230

HighCVSS 7.5/10Last modified Jun 17, 2026

Description

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.

Metrics

CVSS 3.1 7.5/10CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Weakness enumeration

CWE-295

Affected software

Vendor	Product	Versions
n/a	stunnel	stunnel 5.57

References

https://bugzilla.redhat.com/show_bug.cgi?id=1925226Issue Tracking, Third Party Advisory
https://github.com/mtrojnar/stunnel/commit/ebad9ddc4efb2635f37174c9d800d06206f1edf9Patch, Third Party Advisory
https://security.gentoo.org/glsa/202105-02Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1925226Issue Tracking, Third Party Advisory
https://github.com/mtrojnar/stunnel/commit/ebad9ddc4efb2635f37174c9d800d06206f1edf9Patch, Third Party Advisory
https://security.gentoo.org/glsa/202105-02Third Party Advisory

Timeline

Published: Feb 23, 2021
Last modified: Jun 17, 2026
NVD status: Modified

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