FreePBX is an open source IP PBX. Prior to 16.0.6 and 17.0.5.4, the FreePBX Text-To-Speech module allows an authenticated administrator to save a TTS destination name that is HTML-encoded for storage, decoded during dialplan generation, passed as an AGI argument, and used to build filenames inside agi-bin/propolys-tts.agi. The TTS destination name reaches a raw shell-command execution path, allowing arbitrary operating-system command execution as the asterisk service user. This issue is fixed in versions 16.0.6 and 17.0.5.4.