alt Hacker NewsI thought certificate transparency was the thing that was supposed to prevent exactly what this article is describing. What if anything is incorrect about my model of the world in this respect?
Replies
Certificate transparency worked exactly as designed in this case. Monitoring public certificate transparency logs for anomalies is a different story entirely.
By breaking the software facilitating https via ACME itself, no anomalous certificate transparency logs would have needed to have been created at all.
The front door is locked quite tightly with a watchful security camera, but the window has been left unlocked. Also no one is watching the camera feed.
CT indeed worked out pretty well. At least until bots started hammering crt.sh making it unreliable, and those that want to be alerted to newly issued certificated appeared in the logs need to pay for some purpose-built service instead of just adding a relevant query to their feed reader.
Nothing, although it's more mitigate than prevent per se. They simply did not have alerting set up against the CT logs. It is one of the lessons they highlighted in their own postmortem.
Basically, CT did indeed worked as designed, but there was no monitoring by the domain authors (which to be fair there are a dearth of solutions of the time).
On a related note, Let's Encrypt also issued the presumably-interception certificates. This can be possibly something that requires interception at the VPS level (otherwise we already detected the BGP leaks). Presumably, Hetzner was forced to do a raw interception and then redirecting all relevant ports to a middlebox for inspection and CA issuance (and since that the ACME spec is well-defined, they can simply check if the handshake contains the TLS ALPN challenge and then redirect them to special code that will reply with the correct things).