Re-worked the http-form-brute script, the changes include:

- autodetecting form fields is now a bit more robust
- only the password field is mandatory
- HTTP re-directs are followed in case they're detected
- the detection of incorrect login attempts has been changed and supports
  two new arguments (onsucces, onfailure)
[Patrik]

scripts/http-form-brute.nse

@@ -10,6 +10,25 @@ Performs brute force password auditing against http form-based authentication.
 -- guessing. Any successful guesses are stored in the nmap registry, under
 -- the nmap.registry.credentials.http key for other scripts to use.
 --
+-- The script automatically attempts to discover the form field names to
+-- use in order to perform password guessing. If it fails doing so the form
+-- parameters can be supplied using the uservar and passvar arguments.
+--
+-- After attempting to authenticate using a HTTP POST request the script
+-- analyzes the response and attempt to determine whether authentication was
+-- successful or not. The script analyzes this by checking the response using
+-- the following rules:
+--		1. If the response was empty the authentication was successful
+--		2. If the response contains the message passed in the onsuccess
+--		   argument the authentication was successful
+--		3. If no onsuccess argument was passed, and if the response
+--		   does not contain the message passed in the onfailure argument the
+--		   authentication was successful
+--		4. If neither the onsuccess or onfailure argument was passed and the
+--		   response does not contain a password form field authentication
+--		   was successful
+--		5. Authentication failed
+--
 -- @output
 -- PORT     STATE SERVICE REASON
 -- 80/tcp   open  http    syn-ack
@@ -27,17 +46,23 @@ Performs brute force password auditing against http form-based authentication.
 -- @args http-form-brute.path points to the path protected by authentication
 -- @args http-form-brute.hostname sets the host header in case of virtual 
 --       hosting
--- @args http-form-brute.uservar sets the http-variable name that holds the
+-- @args http-form-brute.uservar (optional) sets the http-variable name that
---		 username used to authenticate. A simple autodetection of this variable
+--       holds the username used to authenticate. A simple autodetection of
---       is attempted.
+--       this variable is attempted.
 -- @args http-form-brute.passvar sets the http-variable name that holds the
 --		 password used to authenticate. A simple autodetection of this variable
 --       is attempted.
-
+-- @args http-form-brute.onsuccess (optional) sets the message to expect on
+--		 successful authentication
+-- @args http-form-brute.onfailure (optional) sets the message to expect on
+--		 unsuccessful authentication
 
 --
--- Version 0.1
+-- Version 0.3
 -- Created 07/30/2010 - v0.1 - created by Patrik Karlsson <patrik@cqure.net>
+-- Revised 05/23/2011 - v0.2 - changed so that uservar is optional
+-- Revised 06/05/2011 - v0.3 - major re-write, added onsucces, onfailure and
+--								support for redirects
 --
 
 author = "Patrik Karlsson"
@@ -47,6 +72,7 @@ categories = {"intrusive", "auth"}
 require 'shortport'
 require 'http'
 require 'brute'
+require 'url'
 
 portrule = shortport.port_or_service( {80, 443}, {"http", "https"}, "tcp", "open")
 
@@ -60,7 +86,6 @@ Driver = {
         self.__index = self
 		o.host = nmap.registry.args['http-form-brute.hostname'] or host
 		o.port = port
-		o.path = nmap.registry.args['http-form-brute.path']
 		o.options = options
 		return o
 	end,
@@ -75,18 +100,40 @@ Driver = {
 	login = function( self, username, password )
 		-- we need to supply the no_cache directive, or else the http library
 		-- incorrectly tells us that the authentication was successfull
-		local response = http.post( self.host, self.port, self.path, { no_cache = true }, nil, { [self.options.uservar] = username, [self.options.passvar] = password } )
+		local postparams = { [self.options.passvar] = password }
+		if ( self.options.uservar ) then postparams[self.options.uservar] = username end
+		
+		local response = Driver.postRequest(self.host, self.port, self.options.path, postparams)
+		local success = false
+		
+		-- if we have no response, we were successful
+		if ( not(response.body) ) then
+			success = true
+		-- if we have a response and it matches our onsuccess match, login was successful
+		elseif ( response.body and
+				self.options.onsuccess and 
+				response.body:match(self.options.onsuccess) ) then
+			success = true
+		-- if we have a response and it does not match our onfailure, login was successful
+		elseif ( response.body and
+				not(self.options.onsuccess) and
+				self.options.onfailure and
+				not(response.body:match(self.options.onfailure))) then
+			success = true
+		-- if we have a response and no onfailure or onsuccess match defined 
+		-- and can't find a password field, login was successful
+		elseif ( response.body and
+				not(self.options.onfailure) and
+				not(self.options.onsuccess) and
+				not(response.body:match("input.-type=[\"]*[Pp][Aa][Ss][Ss][Ww][Oo][Rr][Dd][\"]*"))
+				) then
+			success = true
+		end
 
 		-- We check whether the body was empty or that we have a body without our user- and pass-var
-		if ( not( response.body ) or 
+		if ( success ) then
-		   ( response.body and not( response.body:match("name=\"*" .. self.options.uservar ) and response.body:match("name=\"*" .. self.options.passvar ) ) ) ) then
+			nmap.registry['credentials'] = nmap.registry['credentials'] or {}
-		
+			nmap.registry.credentials['http'] = nmap.registry.credentials['http'] or {}
-			if ( not( nmap.registry['credentials'] ) ) then
-				nmap.registry['credentials'] = {}
-			end
-			if ( not( nmap.registry.credentials['http'] ) ) then
-				nmap.registry.credentials['http'] = {}
-			end
 			table.insert( nmap.registry.credentials.http, { username = username, password = password } )
 			return true, brute.Account:new( username, password, "OPEN")
 		end
@@ -99,15 +146,19 @@ Driver = {
 	end,
 	
 	check = function( self )
-		local response = http.get( self.host, self.port, self.path )
+		return true
-				
-		-- do a *very* simple check
-		if ( response.status == 200 and response.body:match("type=\"password\"")) then
-			return true
-		end
-		return false
 	end,
 	
+	postRequest = function( host, port, path, options )
+		local response = http.post( host, port, path, { no_cache = true }, nil, options )
+		local status = ( response and tonumber(response.status) ) or 0
+		if ( status > 300 and status < 400 ) then
+			local new_path = url.absolute(path, response.header.location)
+			response = http.get( host, port, new_path, { no_cache = true } )
+		end
+		return response
+	end,
+		
 }
 
 --- Attempts to auto-detect known form-fields
@@ -117,11 +168,11 @@ local function detectFormFields( host, port, path )
 	local user_field, pass_field
 	
 	if ( response.status == 200 ) then
-		user_field = response.body:match("<input.-name=[\"]-([^\"]-[Uu][Ss][Ee][Rr].-)[\"].->")
+		user_field = response.body:match("<[Ii][Nn][Pp][Uu][Tt].-name=[\"]*([^\"]-[Uu][Ss][Ee][Rr].-)[\"]*.->")
-		pass_field = response.body:match("<input.-name=[\"]-([Pp][Aa][Ss][Ss].-)[\"].->")
+		pass_field = response.body:match("<[Ii][Nn][Pp][Uu][Tt].-name=[\"]*([Pp][Aa][Ss][Ss].-)[\"]*.->")
 
 		if ( not(pass_field) ) then
-			pass_field = response.body:match("<input.-name=[\"]-([^\"]-[Kk][Ee][Yy].-)[\"].->")
+			pass_field = response.body:match("<[Ii][Nn][Pp][Uu][Tt].-name=[\"]-([^\"]-[Kk][Ee][Yy].-)[\"].->")
 		end
 	end
 	
@@ -129,34 +180,65 @@ local function detectFormFields( host, port, path )
 end
 
 action = function( host, port )
-	local uservar = nmap.registry.args['http-form-brute.uservar']
+	local uservar = stdnse.get_script_args('http-form-brute.uservar')
-	local passvar = nmap.registry.args['http-form-brute.passvar']
+	local passvar = stdnse.get_script_args('http-form-brute.passvar')
-  	local path = nmap.registry.args['http-form-brute.path'] or "/"
+  	local path = stdnse.get_script_args('http-form-brute.path') or "/"
-	local status, result, engine, _
+	local force = stdnse.get_script_args("http-form-brute.force")
+	local onsuccess = stdnse.get_script_args("http-form-brute.onsuccess")
+	local onfailure = stdnse.get_script_args("http-form-brute.onfailure")
+	
+	local _
 
+	-- if now fields were given attempt to autodetect
 	if ( not(uservar) and not(passvar) ) then
 		uservar, passvar = detectFormFields( host, port, path )
-	elseif ( not(uservar) ) then
+	-- if now passvar was detected attempt to autodetect
-		uservar, _ = detectFormFields( host, port, path )
 	elseif ( not(passvar) ) then
 		_, passvar = detectFormFields( host, port, path )
 	end
-	if ( not( uservar ) ) then
+	
-		return "  \n  ERROR: No uservar was specified (see http-form-brute.uservar)"
+	-- uservar is optional, so only make sure we have a passvar
-	end
 	if ( not( passvar ) ) then
-		return "  \n  ERROR: No passvar was specified (see http-form-brute.passvar)"
+		return "\n  ERROR: No passvar was specified (see http-form-brute.passvar)"
 	end
 	
-	if ( not(nmap.registry.args['http-form-brute.path']) ) then
+	if ( not(path) ) then
-		return "  \n  ERROR: No path was specified (see http-form-brute.path)"
+		return "\n  ERROR: No path was specified (see http-form-brute.path)"
 	end
-
+	
-	engine = brute.Engine:new( Driver, host, port, { uservar = uservar, passvar = passvar } )
+	if ( onsuccess and onfailure ) then
+		return "\n  ERROR: Either the onsuccess or onfailure argument should be passed, not both."
+	end
+	
+	local options = { [passvar] = "this_is_not_a_valid_password" }
+	if ( uservar ) then options[uservar] = "this_is_not_a_valid_user" end
+	
+	local response = Driver.postRequest( host, port, path, options )
+	if ( not(response) or not(response.body) or response.status ~= 200 ) then
+		return ("\n  ERROR: Failed to retrieve path (%s) from server"):format(path)
+	end
+	
+	-- try to detect onfailure match
+	if ( onfailure and not(response.body:match(onfailure)) ) then
+		return ("\n  ERROR: Failed to match password failure message (%s)"):format(onfailure)
+	elseif ( not(onfailure) and 
+			not(onsuccess) and 
+			not(response.body:match("input.-type=[\"]*[Pp][Aa][Ss][Ss][Ww][Oo][Rr][Dd][\"]*")) ) then
+		return ("\n  ERROR: Failed to detect password form field see (http-form-brute.onsuccess or http-form-brute.onfailure)")
+	end
+	
+	local engine = brute.Engine:new( Driver, host, port, {
+		uservar = uservar, passvar = passvar, 
+		path = path, onsuccess = onsuccess, onfailure = onfailure
+		} 
+	)
 	-- there's a bug in http.lua that does not allow it to be called by
 	-- multiple threads
 	engine:setMaxThreads(1)
-	status, result = engine:start()
+	if ( not(uservar) ) then
+		engine.options:setOption( "passonly", true )
+	end
+	local status, result = engine:start()
 		
 	return result
 end