Don't try to be too helpful

John cares not one whit how many colons are in a hash line, only that
there are enough for the format (at least 2 for regular /etc/passwd, at
least 3 for NTLM, etc). So there is no simple way to programmatically
determine whether a password had a colon or there was just an extra on
the end of the original hash line.

[MSP-9778]
See #2515

lib/msf/core/auxiliary/jtr.rb

@@ -142,12 +142,11 @@ module Auxiliary::JohnTheRipper
           res[:uncracked] = $2.to_i
         end
 
+        # XXX: If the password had : characters in it, we're screwed
+
         bits = line.split(':', -1)
 
-        # If the password had : characters in it, put them back together
-        while bits.length > 7
-          bits[1,2] = bits[1,2].join(":")
-        end
+        # Skip blank passwords
         next if not bits[2]
 
         if (format== 'lm' or format == 'nt')