CVE-2021-20230

Name	CVE-2021-20230
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.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	982578

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
stunnel4 (PTS)	bullseye	3:5.56+dfsg-10	fixed
	bookworm	3:5.68-2+deb12u1	fixed
	sid, trixie	3:5.72-4	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
stunnel4	source	stretch	(not affected)
stunnel4	source	(unstable)	3:5.56+dfsg-8			982578

Notes

[buster] - stunnel4 <no-dsa> (Minor issue)
[stretch] - stunnel4 <not-affected> (Re-ordering of redirect/accept/reject checks performed in stunnel 5.41b8)
https://github.com/mtrojnar/stunnel/commit/ebad9ddc4efb2635f37174c9d800d06206f1edf9
Isolated fix only the changes in src/verify.c:
https://bugzilla.suse.com/show_bug.cgi?id=1177580#c2
https://bugzilla.redhat.com/show_bug.cgi?id=1925226