Script smb-security-mode

Script types: hostrule
Categories: default, discovery, safe

Script Summary

Returns information about the SMB security level determined by SMB.

Here is how to interpret the output:

  • User-level authentication: Each user has a separate username/password that is used to log into the system. This is the default setup of pretty much everything these days.
  • Share-level authentication: The anonymous account should be used to log in, then the password is given (in plaintext) when a share is accessed. All users who have access to the share use this password. This was the original way of doing things, but isn't commonly seen, now. If a server uses share-level security, it is vulnerable to sniffing.
  • Challenge/response passwords supported: If enabled, the server can accept any type of password (plaintext, LM and NTLM, and LMv2 and NTLMv2). If it isn't set, the server can only accept plaintext passwords. Most servers are configured to use challenge/response these days. If a server is configured to accept plaintext passwords, it is vulnerable to sniffing. LM and NTLM are fairly secure, although there are some brute-force attacks against them. Additionally, LM and NTLM can fall victim to man-in-the-middle attacks or relay attacks (see MS08-068 or my writeup of it:
  • Message signing: If required, all messages between the client and server must be signed by a shared key, derived from the password and the server challenge. If supported and not required, message signing is negotiated between clients and servers and used if both support and request it. By default, Windows clients don't sign messages, so if message signing isn't required by the server, messages probably won't be signed; additionally, if performing a man-in-the-middle attack, an attacker can negotiate no message signing. If message signing isn't required, the server is vulnerable to man-in-the-middle attacks or SMB-relay attacks.

This script will allow you to use the smb* script arguments (to set the username and password, etc.), but it probably won't ever require them.

Script Arguments

randomseed, smbbasic, smbport, smbsign

See the documentation for the smb library.

smbdomain, smbhash, smbnoguest, smbpassword, smbtype, smbusername

See the documentation for the smbauth library.

Example Usage

nmap --script smb-security-mode.nse -p445
sudo nmap -sU -sS --script smb-security-mode.nse -p U:137,T:139

Script Output

| smb-security-mode:
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)



  • Ron Bowes

License: Same as Nmap--See