Land rapid7#2578, @wchen-r7's [FixRM rapid7#8525]

Author: jvazquez-r7

modules/post/windows/gather/enum_ie.rb

@@ -319,8 +319,15 @@ def run
         if val_arr.include?(hash)
           data = registry_getvaldata(regpath, hash)
           dec = decrypt_reg(url, data)
+
+          # If CryptUnprotectData fails, decrypt_reg() will return "", and unpack() will end up
+          # returning an array of nils. If this happens, we can cause an "undefined method
+          # `+' for NilClass." when we try to calculate the offset, and this causes the module to die.
+          next if dec.empty?
+
           #decode data and add to creds array
           header = dec.unpack("VVVVVV")
+
           offset = header[0] + header[1] #offset to start of data
           cnt = header[5]/2 # of username/password combinations
           secrets = dec[offset,dec.length-(offset + 1)].split("\x00\x00")