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.
Overview
- Severity
- High (CVSS 7.5)
- CVSS Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Exploit Status
- Not Exploited
- Patch Tuesday
- 2021-Feb
- Released
- 2022-01-19
- EPSS Score
- 0.21% (percentile: 43.3%)
FAQ
Is Azure Linux the only Microsoft product that includes this open-source library and is therefore potentially affected by this vulnerability?
One of the main benefits to our customers who choose to use the Azure Linux distro is the commitment to keep it up to date with the most recent and most secure versions of the open source libraries with which the distro is composed. Microsoft is committed to transparency in this work which is why we began publishing CSAF/VEX in October 2025. See this blog post for more information. If impact to additional products is identified, we will update the CVE to reflect this.
Affected Products (1)
Other
Revision History
- 2022-01-19: Information published.