Improved error handling

modules/exploits/linux/http/docker_daemon_tcp.rb

@@ -61,7 +61,7 @@ class MetasploitModule < Msf::Exploit::Remote
       'method'  => 'GET',
       'uri'     => normalize_uri('images', 'json')
     )
-    return unless res.code == 200 and res.body.include? image_id
+    return unless res and res.code == 200 and res.body.include? image_id
 
     res
   end
@@ -129,14 +129,24 @@ class MetasploitModule < Msf::Exploit::Remote
       'uri'      => normalize_uri('containers', 'json'),
       'headers'  => { 'Accept' => 'application/json' }
     )
-    return Exploit::CheckCode::Vulnerable if res.code == 200 and res.headers['Server'].include? 'Docker'
+
+    if res.nil?
+      print_error('Failed to connect to the target')
+      return Exploit::CheckCode::Unknown
+    end
+
+    if res and res.code == 200 and res.headers['Server'].include? 'Docker'
+      return Exploit::CheckCode::Vulnerable
+    end
 
     Exploit::CheckCode::Safe
   end
 
   def exploit
     # check if target is vulnerable
-    fail_with(Failure::Unknown, 'Failed to connect to the targeturi') if check.nil?
+    unless check == Exploit::CheckCode::Appears
+      fail_with(Failure::Unknown, 'Failed to connect to the target')
+    end
 
     # check if image is not available, pull it or fail out
     image_id = datastore['DOCKERIMAGE']