Vulnerability Details

Nmap NSE 6.01: smb-brute

Published: 2013-02-28 13:29:58

CVSS Base Vector:
AV:N/AC:L/Au:N/C:P/I:P/A:P

Detection Type:
remote_analysis

Summary:
Attempts to guess username/password combinations over SMB, storing discovered combinations for use in other scripts. Every attempt will be made to get a valid list of users and to verify each username before actually using them. When a username is discovered, besides being printed, it is also saved in the Nmap Windows Registry so other Nmap scripts can use it. That means that if you're going to run 'smb-brute.nse', you should run other 'smb' scripts you want. This checks passwords in a case-insensitive way, determining case after a password is found, for Windows versions before Vista. This script is specifically targeted towards security auditors or penetration testers. One example of its use, suggested by Brandon Enright, was hooking up 'smb-brute.nse' to the database of usernames and passwords used by the Conficker worm (the password list can be found at the references), among other places. Then, the network is scanned and all systems that would be infected by Conficker are discovered. From the penetration tester perspective its use is pretty obvious. By discovering weak passwords on SMB, a protocol that's well suited for bruteforcing, access to a system can be gained. Further, passwords discovered against Windows with SMB might also be used on Linux or MySQL or custom Web applications. Discovering a password greatly beneficial for a pen-tester. This script uses a lot of little tricks that I (Ron Bowes) describe in detail in a blog posting (see references). The tricks will be summarized here, but that blog is the best place to learn more. Usernames and passwords are initially taken from the unpwdb library. If possible, the usernames are verified as existing by taking advantage of Windows' odd behaviour with invalid username and invalid password responses. As soon as it is able, this script will download a full list of usernames from actual accounts only. SYNTAX: userdb: The filename of an alternate username database. brutelimit: Limits the number of usernames checked in the script. In some domains, it's possible to end up with 10.000+ usernames on each server. By default, this will be '5000', which should be higher than most servers and also prevent infinite loops or other weird things. This will only affect the user list pulled from the server, not the username list. randomseed: Set to a value to change the filenames/service names that are randomly generated. unpwdb.timelimit: The maximum amount of time that any iterator will run before stopping. The value is in seconds by default and you can follow it with 'ms', 's', 'm', or 'h' for milliseconds, seconds, minutes, or hours. For example, 'unpwdb.timelimit=30m' or 'unpwdb.timelimit=.5h' for 30 minutes. The default depends on the timing template level (see the module description). Use the value '0' to disable the time limit. unpwdb.userlimit: The maximum number of usernames 'usernames' will return (default unlimited). smblockout: This argument will force the script to continue if it locks out an account or thinks it will lock out an account. smbport: Override the default port choice. If 'smbport' is open, it's used. It's assumed to be the same protocol as port 445, not port 139. Since it probably isn't possible to change Windows' ports normally, this is mostly useful if you're bouncing through a relay or something. passdb: The filename of an alternate password database. smbbasic: Forces the authentication to use basic security, as opposed to 'extended security'. Against most modern systems, extended security should work, but there may be cases where you want to force basic. There's a chance that you'll get better results for enumerating users if you turn on basic authentication. smbsign: Controls whether or not server signatures are checked in SMB packets. By default, on Windows, server signatures aren't enabled or required. By default, this library will always sign packets if it knows how, and will check signatures if the server says to. Possible values are: - 'force': Always check server signatures, even if server says it doesn't support them (will probably fail, but is technically more secure). - 'negotiate': [default] Use signatures if server supports them. - 'ignore': Never check server signatures. Not recommended. - 'disable': Don't send signatures, at all, and don't check the server's. not recommended. More information on signatures can be found in 'smbauth.lua'. canaries: Sets the number of tests to do to attempt to lock out the first account. This will lock out the first account without locking out the rest of the accounts. The default is 3, which will only trigger strict lockouts, but will also bump the canary account up far enough to detect a lockout well before other accounts are hit. unpwdb.passlimit: The maximum number of passwords 'passwords' will return (default unlimited).

Solution Type:
Mitigation

References:

http://www.skullsecurity.org/blog/?p=164
http://www.skullsecurity.org/wiki/index.php/Passwords

Severity
High
CVSS Score
7.5
Published
2013-02-28
Modified
2018-10-26
Category
Nmap NSE

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