CVE-2021-20230
7.5 · HIGHOverview
CVE-2021-20230 is a high-severity vulnerability affecting stunnel stunnel. It was published on February 23, 2021 and has a CVSS 3.1 base score of 7.5 (HIGH).
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical 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.
Remediation
Check the references section for vendor advisories and patches from stunnel. Update stunnel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| stunnel | stunnel | >= 0, < 5.57 | Affected |
References
Frequently Asked Questions
What is CVE-2021-20230?
CVE-2021-20230 is a high-severity vulnerability affecting stunnel stunnel. It was published on February 23, 2021 and has a CVSS 3.1 base score of 7.5 (HIGH).
How severe is CVE-2021-20230?
This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2021-20230?
Check the references section for vendor advisories and patches from stunnel. Update stunnel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2021-20230?
CyberStrike's AI-powered security agents can automatically detect CVE-2021-20230 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
Automated penetration testing that runs continuously, not just quarterly.
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Browser-based exploitation validates findings with real proof-of-concept.
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