CVE-2021-20230

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.

• CWE-295

• 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

Published

Feb 23, 2021

Last Modified

Jun 17, 2026

Status

Modified

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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