Process and analysis
What is Attack surface?
Everything an outsider can reach and attempt to use, which is why an inventory is the cheapest proactive work there is.
The attack surface is everything an outsider could reach and try to use: exposed servers and services, web applications, login pages, VPN gateways, cloud storage, third-party connections and the people who can be phished.
Attack surface management is the work of finding that surface before attackers do. Most of the value comes from discovering what nobody remembered running, such as a forgotten test server or an old marketing site, because those are the systems that never get patched.