I'd bet they could absolutely proxy large parts of people and make use of these certs. I wonder how much are CT logs scrutinized, would these "rogue" certs be found easily because we can't find traces of them being generated by letsencrypt ? Browsers checks CRLs but are they checking CT logs to be ensure the cert they're checking was logged ?
They couldn't do that at scale without being detected, no. There are various people actively looking for this, and the existing tooling makes it easy to detect.
>Browsers checks CRLs but are they checking CT logs to be ensure the cert they're checking was logged ?
Yes, all modern browsers require certificates to be in the CT logs in order for them to be accepted.
