AudioCodes Fax Server and Auto-Attendant IVR appliances versions up to and including 2.6.23 include a web administration component that controls back-end Windows services using helper batch scripts located under C:\\F2MAdmin\\F2E\\AudioCodes_files\\utils\\Services. When certain service actions are requested through ajaxPost.php, these scripts are invoked by PHP using system() under the NT AUTHORITY\\SYSTEM account. The batch files in this directory are writable by any authenticated local user due to overly permissive ACLs, allowing them to replace script contents with arbitrary commands.

On the next service start/stop operation, the modified script is executed as SYSTEM, enabling elevation of local privileges.