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RedHuntLabs scanned 220 million subdomains in 2020. Found over 400,000 vulnerable to takeover. But that is DNS. For SMB, the equivalent statistic is this: every Windows machine that attempts to resolve a hostname via LLMNR or NBT-NS will happily authenticate to any responder on the network. No exploit needed. No vulnerability. Just a protocol doing what it was designed to do. And you sitting there with Responder running.
The attack is called Forced Authentication. You do not attack the target. You make the target come to you. A user mistypes a share name. \\fileserver\reports becomes \\fileserve\reports. The DNS lookup fails. The machine falls back to LLMNR multicast. Your Responder answers. The machine authenticates to your fake server. You capture the NTLMv2 hash. Done.
The hash is captured. Now you have two choices. Crack it offline with hashcat mode 5600. Or relay it to another host where that user has admin rights. If the user is a domain admin who mistyped a share name, you just captured the keys to the kingdom. No exploit. No privilege escalation. Just patience and a running Responder.
For relay to work, SMB signing must be disabled on the target. If signing is required, the relay fails. Check with nmap --script smb2-security-mode. Also, you must disable SMB in your Responder config (SMB = Off in /etc/responder/Responder.conf) before running ntlmrelayx, or the two tools conflict.
The beauty of this attack is its passivity. You do not scan. You do not brute force. You do not exploit. You sit on the network and wait. Someone, somewhere, will mistype a hostname. Their machine will broadcast. You will answer. And their hash will be yours. In a domain with five hundred users, you will capture something within fifteen minutes. I have never run an engagement where Responder came back empty.
Finish the lesson once you have worked through the material. This awards ★ 40 XP.