Internal Domain Names

I found out last week how easily one can get a certificate from GoDaddy with a SAN (Subject Alternative Name) for a non-registered domains name. This would include domains that end in .dom or .local that do not have a public registrar. Since GoDaddy cannot retrieve a WHOIS record for the domain, their authorization email only needs to be approved by the account that requests the certificate. This vulnerability removes a significant barrier for a man-in-the-middle attack, since the certificate would be trusted and the name would match the URL requested by the users.

Additionally, Office 365 AD Sync (needed for password synchronization) will not work with these type of non-registerable DNS names in a UPN suffix. While the UPN suffix can be changed to be different than the domain name, the problem would not exist for domains that use names like “internal.registereddomain.com”.

Networking SAN Office 365 DNS