Comment by hlandau
3 years ago
Both you and the grandparent are correct in that both propose viable attacks; it is a known fact (and not news to any expert in the space) that "domain validation" certificates are vulnerable to "global" MitM in which an attacker can intercept all traffic to a domain (and therefore intercept the validation probes). A situation in which a service's hosting company is sitting on their "front door" (so to speak) and MitMing all traffic that goes their way is exactly such a situation (hence my recommended mitigation).
Hosting company is not the only one who can do MitM; any ISP through which the traffic passes can do that as well; and if there are backdoors in foreign network equipment then the manufacturer of equipment can do MitM too.
This is false, because Let’s Encrypt uses servers in multiple places to get a mix of routing paths to eliminate it as an attack vector.