While performing a pentest, if you discover a server running the SMB protocol  you can test if it’s vulnerable to anonymous connection (also called null session) and then glean a lot of informations with a RPC client. Nmap is usefull to locate that kind of service:

smb null session

Now you can try to interact with the remote machine with the help of rpcclient. To perform a null session you have to specify an empty user and an empty password. If the host is not vulnerable, you will get the following error:

$ rpcclient -U "" 192.168.1.31 Enter 's password: could not initialise lsa pipe. Error was NT_STATUS_ACCESS_DENIED could not obtain sid for domain WORKGROUP error: NT_STATUS_ACCESS_DENIED

But if the host is vulnerable you will immediatly get a prompt:

$ rpcclient -U "" 192.168.1.18 Enter 's password: rpcclient $>

If you connect successfully, you can use help to see the list of available commands (anyway tab works for autocompletion). Below some examples of the most used.

Basic server infos:

rpcclient $> srvinfo LUIGI Wk Sv PrQ Unx NT SNT nintendo server platform_id : 500 os version : 4.9 server type : 0x809a03

Users enumeration:

rpcclient $> enumdomusers user:[admin] rid:[0x3ec] user:[Administrator] rid:[0x1f4] user:[Guest] rid:[0x1f5] user:[lisa] rid:[0x3f1] user:[mark] rid:[0x3f2]</pre>

Groups enumeration:

rpcclient $> enumalsgroups builtin group:[Administrators] rid:[0x220] group:[Backup Operators] rid:[0x227] group:[Guests] rid:[0x222] group:[Power Users] rid:[0x223] group:[Users] rid:[0x221]

Privileges of the connected user:

``` rpcclient $> enumprivs found 8 privileges

SeMachineAccountPrivilege 0:6 (0x0:0x6) SeTakeOwnershipPrivilege 0:9 (0x0:0x9) SeBackupPrivilege 0:17 (0x0:0x11) SeRestorePrivilege 0:18 (0x0:0x12) SeRemoteShutdownPrivilege 0:24 (0x0:0x18) SePrintOperatorPrivilege 0:4097 (0x0:0x1001) SeAddUsersPrivilege 0:4098 (0x0:0x1002) SeDiskOperatorPrivilege 0:4099 (0x0:0x1003) ```

Shares enumeration:

rpcclient $> netshareenum netname: IPC$ remark: IPC Service path: C:\tmp password: netname: Lisa Share remark: Lisa Docs path: C:\home\lisa\files password:

enum4linux is the perfect tool to automate null session attacks. According to the documentation : “[…] this script is basically just a wrapper around rpcclient, net, nmblookup and smbclient […]”.