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No username. No password. Just a connection. That is all a null session requires. And on misconfigured SMB servers, it gives you share listings, user enumerations, group memberships, password policies, and sometimes file contents. I have seen domain environments where every workstation allowed null sessions. Every single one. The admin had no idea.
READ, WRITE on the notes share. With a null session. No credentials at all. smbmap shows permissions per share in a clean table. From here you can browse directories recursively with -r, download files with --download, and upload with --upload. All without authenticating.
Five domain users enumerated with zero credentials. The '%' represents an empty password. From here you can query user details with queryuser, enumerate groups with enumdomgroups, check password policy with getdompwinfo. This is your username list for the password spray you will run next.
enum4linux-ng automates all of this. One command: ./enum4linux-ng.py 10.10.11.45 -A -C. It runs nmblookup, net, rpcclient, and smbclient under the hood and gives you a formatted report of workgroup, users, groups, shares, OS info, and password policy. Use it for speed. Use the individual tools when you need precision.
Null sessions are the low-hanging fruit of SMB attacks. They require nothing from you except a network connection. Always try them first. If the server rejects null sessions, you move to credential-based attacks. But if it accepts them, you just saved yourself an hour of brute forcing. Check it on every single host you encounter.
Finish the lesson once you have worked through the material. This awards ★ 30 XP.