Vulnerability · Published Feb 23, 2021 · Assigned by redhat

CVE-2021-20230

High 7.5

In plain English

A high-severity improper certificate validation in stunnel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.2% (higher than 68% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS NVD)7.5High

Exploit odds (30 days)1.2%top 32.2% of all CVEs

Exploited in the wildNo reportsnot in CISA KEV

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
AlmaLinux:8	stunnel	5.56-5.el8_3	ALSA-2021:0618
Debian:12	stunnel4	3:5.56+dfsg-8	DEBIAN-CVE-2021-20230
Debian:13	stunnel4	3:5.56+dfsg-8	DEBIAN-CVE-2021-20230
Rocky Linux:8	stunnel	0:5.56-5.el8_3	RLSA-2021:0618

Affected products (as reported)

Vendor	Product	Versions
n/a	stunnel	stunnel 5.57

Weakness: CWE-295

References

https://bugzilla.redhat.com/show_bug.cgi?id=1925226 x_refsource_MISC
https://github.com/mtrojnar/stunnel/commit/ebad9ddc4efb2635f37174c9d800d06206f1edf9 x_refsource_MISC
GLSA-202105-02 vendor-advisory, x_refsource_GENTOO