o [NSE] Added a new library for ASN.1 parsing and adapted the SNMP library to

make use of it. Added 5 scripts that use the new libraries:
  - snmp-netstat shows listening and connected sockets
  - snmp-processes shows process information including name, pid, path and 
    parameters
  - snmp-win32-services shows the names of running Windows services
  - snmp-win32-shares shows the names and path of Windows shares
  - snmp-win32-software shows a list of installed Windows software
  - snmp-win32-users shows a list of local Windows users

scripts/snmp-win32-users.nse

@@ -0,0 +1,118 @@
+description = [[
+Attempts to enumerate User Accounts through SNMP
+]]
+
+---
+-- @output
+-- | snmp-win32-users:  
+-- |   Administrator
+-- |   Guest
+-- |   IUSR_EDUSRV011
+-- |   IWAM_EDUSRV011
+-- |   SUPPORT_388945a0
+-- |   Tomcat
+-- |   db2admin
+-- |   ldaptest
+-- |_  patrik
+
+
+author = "Patrik Karlsson"
+license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
+categories = {"default", "discovery", "safe"}
+dependencies = {"snmp-brute"}
+
+-- Version 0.2
+-- Created 01/15/2010 - v0.1 - created by Patrik Karlsson <patrik@cqure.net>
+-- Revised 01/19/2010 - v0.2 - fixed loop that would occure if a mib did not exist
+
+require "shortport"
+require "snmp"
+
+portrule = shortport.portnumber(161, "udp", {"open", "open|filtered"})
+
+--- Walks the MIB Tree
+--
+-- @param socket socket already connected to the server
+-- @base_oid string containing the base object ID to walk
+-- @return table containing <code>oid</code> and <code>value</code>
+function snmp_walk( socket, base_oid )
+	
+	local catch = function() socket:close()	end
+	local try = nmap.new_try(catch)	
+
+	local snmp_table = {}
+	local oid = base_oid
+	
+	while ( true ) do
+		
+		local value, response, snmpdata, options, item = nil, nil, nil, {}, {}
+		options.reqId = 28428 -- unnecessary?
+		payload = snmp.encode( snmp.buildPacket( snmp.buildGetNextRequest(options, oid) ) )
+
+		try(socket:send(payload))
+		response = try( socket:receive_bytes(1) )
+	
+		snmpdata = snmp.fetchResponseValues( response )
+		
+		value = snmpdata[1][1]
+		oid  = snmpdata[1][2]
+		
+		if not oid:match( base_oid ) or base_oid == oid then
+			break
+		end
+		
+		item.oid = oid
+		item.value = value
+		
+		table.insert( snmp_table, item )
+		
+	end
+
+	socket:close()
+	snmp_table.baseoid = base_oid
+
+	return snmp_table
+	
+end
+
+--- Processes the table and creates the script output
+--
+-- @param tbl table containing <code>oid</code> and <code>value</code>
+-- @return table suitable for <code>stdnse.format_output</code>
+function process_answer( tbl )
+
+	local new_tab = {}
+
+	for _, v in ipairs( tbl ) do
+		table.insert( new_tab, v.value )
+	end
+	
+	table.sort( new_tab )
+	
+	return new_tab
+	
+end
+
+action = function(host, port)
+
+	local socket = nmap.new_socket()
+	local catch = function() socket:close()	end
+	local try = nmap.new_try(catch)	
+	local snmpoid = "1.3.6.1.4.1.77.1.2.25"
+	local users = {}
+
+	socket:set_timeout(5000)
+	try(socket:connect(host.ip, port.number, "udp"))
+	
+	users = snmp_walk( socket, snmpoid )
+	users = process_answer( users )
+
+	if ( users == nil ) or ( #users == 0 ) then
+		return
+	end
+	
+	nmap.set_port_state(host, port, "open")
+
+	return stdnse.format_output( true, users )
+end
+