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NetBIOS Auditing Tool Release



As of February 16th Secure Networks Inc. has released a free (GPL`d) 


NetBIOS auditing tool for use both on WindowsNT and UNIX platforms. 


The tool itself is designed to test NetBIOS file-sharing configurations as 


well as Password integrity of remote stations. 


The toolset is available via the following channels: 


ftp://ftp.secnet.com/pub/tools/nat10/nat10bin.zip (For NT and Win 95 binaries) 


ftp://ftp.secnet.com/pub/tools/nat10/nat10.tgz (For full source) 


http://www.secnet.com/ntinfo/ntaudit.html A technical description of how the NetBIOS auditing tool works follows. 


The NetBIOS Auditing Tool (NAT) is designed to explore the NETBIOS file-sharing 


services offered by the target system. It implements a stepwise approach to 


gather information and attempt to obtain file system-level access as though 


it were a legitimate local client. 


The major steps are as follows: 


A UDP status query is sent to the target, which usually elicits a reply 


containing the Netbios "computer name". This is needed to establish a session. 


The reply also can contain other information such as the workgroup and account 


names of the machine`s users. This part of the program needs root privilege to 


listen for replies on UDP port 137, since the reply is usually sent back to UDP 


port 137 even if the original query came from some different port. 


TCP connections are made to the target`s Netbios port [139], and session 


requests using the derived computer name are sent across. Various guesses at 


the computer name are also used, in case the status query failed or returned 


incomplete information. If all such attempts to establish a session fail, 


the host is assumed invulnerable to NETBIOS attacks even if TCP port 139 was 


reachable. 


Provided a connection is established Netbios "protocol levels" are now 


negotiated across the new connection. This establishes various modes and 


capabilities the client and server can use with each other, such as password 


encryption and if the server uses user-level or share-level Security. The 


usable protocol level is deliberately limited to LANMAN version 2 in this 


case, since that protocol is somewhat simpler and uses a smaller password 


keyspace than NT. 


If the server requires further session setup to establish credentials, various 


defaults are attempted. Completely blank usernames and passwords are often 


allowed to set up "guest" connections to a server; if this fails then guesses 


are tried using fairly standard account names such as ADMINISTRATOR, and some 


of the names returned from the status query. Extensive username/password 


checking is NOT done at this point, since the aim is just to get the session 


established, but it should be noted that if this phase is reached at all MANY 


more guesses can be attempted and likely without the owner of the target 


being immediately aware of it. 


Once the session is fully set up, transactions are performed to collect more 


information about the server including any file system "shares" it offers. 


Attempts are then made to connect to all listed file system shares and some 


potentially unlisted ones. If the server requires passwords for the shares, 


defaults are attempted as described above for session setup. Any successful 


connections are then explored for writeability and some well-known file-naming 


problems [the ".." class of bugs]. 


If a NETBIOS session can be established at all via TCP port 139, the target is 


declared "vulnerable" with the remaining question being to what extent. 


Information is collected under the appropriate vulnerability at most of 


these steps, since any point along the way be blocked by the Security 


configurations of the target. Most Microsoft-OS based servers and Unix SAMBA 


will yield computer names and share lists, but not allow actual file-sharing 


connections without a valid username and/or password. A remote connection to 


a share is therefore a possibly serious Security problem, and a connection 


that allows WRITING to the share almost certainly so. Printer and other 


"device" services offered by the server are currently ignored. 


For more information about NAT see: 


http://www.secnet.com/ntinfo/ntaudit.html - Oliver Friedrichs 




---


Secure Networks Incorporated. Calgary, Alberta, Canada, (403) 262-9211 


yaya 


http://fink.sourceforge.net/pdb/package.php/nat

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Tuesday, November 12th, 2002 at 12th:21:08 PM

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