I disagree. It's a fatal flaw in TLS-SNI-01/02. Here's why: All of the information required to solve the challenge is in the attackers control. SAN-A and SAN-B

I disagree. It's a fatal flaw in TLS-SNI-01/02. Here's why: All of the information required to solve the challenge is in the attackers control. SAN-A and SAN-B (in v02) are known by the attacker. And no action or information from the target domain is required to solve the challenge. Every shared hosting provider and CDN that lets you pick a domain and upload a custom certificate can be used to solve the challenge. Your solution of restricting it to ip = one domain just reduces the vulnerable sites to sites that don't use LE and are on a shared provider. (Also note, if the provider does not implement LE.. then they are vulnerable to this attack against all of the customers.. with your solution: 1 customer for each IP owned by the service) As long as SNI is part of the TLS standard, it is incorrect to assume IP = domain ownership.