In this chapter, we learned about a configuration management error called a sub-domain takeover, that is, a method that takes control of a forgotten sub-domain.

The impact is great for a domain's real owner, and although maintaining an updated DNS database can be easy, it's often complicated for bigger organizations.

To conclude, we learned the following about sub-domain takeovers:

• They are originated by a registry in the DNS service that, at some point in time, has been forgotten, meaning another user can register it
• Mitigation is easy—simply delete the registry
• There are a bunch of tools available for monitoring the DNS service; however, automated monitoring can complicate things
• Discovering such vulnerabilities is expensive, both financially and in relation to time and resources