In my experience it's equally likely they just don't do validation to begin with. For example, my Elk M1XEP (physical security system's Ethernet expander) runs a configuration server with and without TLS. They recommend with, but it uses a self-signed certificate, and the crappy VB.NET configuration program doesn't validate the cert in any way, so it can be trivially MITMed. The Elk M1XEP also can connect to a user-chosen alarm monitoring service ("central station") over the Internet. I don't think it uses TLS at all for this. I think there's optional shared secret auth/encryption?
WalterGR•37m ago
https://news.ycombinator.com/item?id=50166579 - “eMudhra intermediate CA compromise” - 947 points | 19 hours ago | 408 comments
https://news.ycombinator.com/item?id=50177916 - "Eight Bits of Trust; eMudhra's CA keys cracked in milliseconds" - 604 points | 7 hours ago | 270 comments