Open WebUI is a self-hosted artificial intelligence platform designed for offline operation. A flaw exists in the speech-to-text transcription endpoint where an unsanitized filename field allows any authenticated, non-admin user to trigger a `FileNotFoundError`. The error message, including the server's absolute `DATA DIR` path, is then returned in the HTTP 400 response body, leading to information disclosure on default deployments. The issue stems from a lack of path sanitization when extracting the file extension from the filename and constructing the file path. Specifically, the `file.filename.split(".")[-1]` function is used without any sanitization, and the resulting value is concatenated into a filesystem path. This allows an attacker to craft a filename containing directory traversal sequences (e.g., `audio./etc/passwd`) to reveal the server's absolute path. The vulnerability is present in the `backend/open webui/routers/audio.py` file, at line 1197, and is triggered when attempting to open a file with a malicious filename. The MIME-type guard does not prevent this issue.