Recently krebsonsecurity published an article on the sale of the domain name corp.com to Microsoft. This sale resolves an important security concern caused by many IT professionals following default configuration guidelines a bit too closely. In the past, Microsoft documentation used the example domain of “corp”, short for corporation, in much of their documentation and didn’t clearly recommend to users to use their own name instead. This led many admins to set up their private company domain with the domain “corp.” Because corp.com was a legitimately registered domain, it could cause a configuration vulnerability on those networks if users were to take their laptops off of the private network or if the local DNS server suddenly became unreachable. Specifically, if the previous owner of corp.com wanted to be malicious, they could set up a server and listen for these errant connections then attempt to steal information ranging from authentication details to file uploads.
Today, Microsoft doesn’t allow signal level domain names, you must use a TLD (Top Level Domain) with your domain name, like “example.com” instead of just your domain name by itself like “example” Microsoft changed their documentation, but older domains may still use signal level domains. While “corp” may be the most popular domain, many other domains don’t go to trusted websites. Test[.]com for example, leads to a website of unknown security. Administrators should make sure they carefully choose their domain names when setting up a new Active Directory or LDAP environment. Any domain name conflict may cause users to access the wrong resources or give private information to the wrong group.
When creating a domain, ensure you don’t conflict with any other public domains. For domains used for testing, and domains that will never become public you can stay secure with “.local” or “.test” But setting up a domain with common words like “local.local” may conflict if you merge the domain with another domain using the same configuration. Best practices for security and usability recommend you register the domain even if used locally. For more on selecting a domain name see the Microsoft documentation.
It is common for improper documentation to cause misconfigurations. The Internet Assigned Numbers Authority (IANA) governs domain name usage and specifically reserves “example.com”, “example.org” and “.example” for use in documentation. Technical writers who create documentation that involves domain names should never use any other domain as an example, not everyone follows this rule and sometimes just the “example” domain names may not be sufficient. Sysadmins should not, of course, use these example names in their production setups, but at least in the event someone uses the reserved example domains they won’t resolve to an unknown party. Either way, when configurating a new domain, ensure you use a unique name and not one used in any documentation.