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Identifying Let’s Encrypt Revoked Certificates

Let’s Encrypt is a free, automated, open certificate authority (CA) run for the public’s benefit as a service from the Internet Security Research Group (ISRG). It provides free digital certificates to enable HTTPS (SSL/TLS) for websites via user-friendly means.

Earlier this week, Let’s Encrypt announced that a bug in its validation code forced it to revoke more than 3 million certificates. The bug allowed subscribers (under specific circumstances and for a limited period) to issue certificates to a domain name even after the domain name holder explicitly prohibited the issuance of certificates through the use of DNS CAA.

This blog explains the implications of the incident. It provides details on the impact it can have on organizations utilizing Let’s Encrypt revoked certificates. It outlines steps for remediation and provides a link to Qualys CertView, a free tool that can be used to identify all affected certificates in users’ environments.

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