don't store less accurate nmap fingerprints, see #4099

git-svn-id: file:///home/svn/framework3/trunk@12302 4d416f70-5f16-0410-b530-b9f4589650da

lib/rex/parser/nmap_xml.rb

@@ -70,10 +70,18 @@ class NmapXMLStreamParser
 				@host["addr"] = attributes["addr"]
 			end
 		when "osclass"
+			# If there is more than one, take the highest accuracy.  In case of
+			# a tie, this will have the effect of taking the last one in the
+			# list.  Last is really no better than first but nmap appears to
+			# put OSes in chronological order, at least for Windows.
+			# Accordingly, this will report XP instead of 2000, 7 instead of
+			# Vista, etc, when each has the same accuracy.
+			if (@host["os_accuracy"].to_i <= attributes["accuracy"].to_i)
 				@host["os_vendor"]   = attributes["vendor"]
 				@host["os_family"]   = attributes["osfamily"]
 				@host["os_version"]  = attributes["osgen"]
 				@host["os_accuracy"] = attributes["accuracy"]
+			end
 		when "osmatch"
 			if(attributes["accuracy"].to_i == 100)
 				@host["os_match"] = attributes["name"]