Let's Encrypt certificate used in malversiting

We'd better get used to a world where malicious traffic is encrypted too.

According to some people, myself included, Let's Encrypt was one of the best things that happened to the Internet in 2015. Now that, as of December, the service is in public beta, anyone can register certificates for domains they own, in a process that is both easy and free.

Cybercriminals have noticed this too, and rather unsurprisingly, Trend Micro reports that a certificate issued by Let's Encrypt was used in an Angler exploit kit-powered malvertising campaign, to make the malicious advertisements harder to detect.

What makes this case particularly interesting is the fact that the domain for which the certificate was issued was the subdomain of a legitimate site, whose DNS was compromised. As domain-based reputation isn't usually granular enough to distinguish between subdomains, this could have helped them avoid detection even further.

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