example persistence cleanup updates

Author: h00die

modules/exploits/example_linux_persistence.rb

@@ -67,7 +67,8 @@ def initialize(info = {})
           [ 'OSVDB', '12345' ],
           [ 'EDB', '12345' ],
           [ 'URL', 'http://www.example.com'],
-          [ 'CVE', '1978-1234']
+          [ 'CVE', '1978-1234'],
+          ['ATT&CK', Mitre::Attack::Technique::T1547_013_XDG_AUTOSTART_ENTRIES], # https://github.com/rapid7/metasploit-framework/pull/20289
         ],
         'DisclosureDate' => '2023-11-29',
         # Note that DefaultTarget refers to the index of an item in Targets, rather than name.
@@ -114,8 +115,8 @@ def install_persistence
     else
       upload_and_chmodx backdoor, generate_payload_exe
     end
-    # add removing the file to the cleanup script
-    @clean_up_rc << "rm #{backdoor}\n"
+    # add removing the file to the cleanup script. The script starts as nil, so we want to overwrite it to a string
+    @clean_up_rc = "rm #{backdoor}\n"
 
     # back up an example file that we're going to write into so we can restore it
     # in our cleanup efforts