Attackers commonly create look-alike websites for phishing campaigns.

To make their impersonation attempts more convincing, attackers will add a digital certificate to the server linked in their phishing email. In the past few years, digital certificates became attainable at no cost, making it even easier for attackers.

For security practitioners, however, there’s a positive side to this trend—attackers leave a trail of breadcrumbs in the form of certificates. Censys pulls data from those certificates, which allows you to find illegitimate servers and update your security filters to block attacker domains.

These mitigations will help prevent your users and customers from being phished or potentially downloading malware from a site they think is being hosted by your organization.

Find valid TLS/SSL certificates that contain domain names you own


Search for certificates that contain one or more domains or subdomains that you own. Then filter out expired and self-signed certificates.

You can also check to see if Censys saw the certificate when scanning IP addresses.



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Valid certificates with “gm.com” found in one or more name fields in the certificate

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Case Study

A National Financial Institution Uses Censys to Fight Certificate Impersonation

“What looking at the certificate data allows us to do is to see all the way down to the subdomain. So you could be looking at a domain that has a good reputation and an adversary takes over an aspect of that domain, insert our institution into the certificate and craft a phishing site. The Censys scans help us locate those exploits and mitigate the risk.”

Read the case study
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