The vulnerability allows an attacker to exploit the upload function to read arbitrary files on the server. By intercepting the WebSocket request during a file upload and modifying the file path, the attacker can trick the server into copying and providing access to any file on the system. This can lead to exposure of sensitive information such as configuration files, credentials, and user data, which can be leveraged for further attacks.

An attacker uploads a file using the upload function and intercepts the WebSocket request. They modify the file path in the request to point to a sensitive file on the server, such as config.py. The server processes the request, copies the specified file to the private_upload folder, and provides a path to access the copied file. The attacker then accesses the file via a GET request, successfully reading the contents of the sensitive file.

Any user of the software who has access to the upload function is affected by this vulnerability. This includes both authenticated and unauthenticated users, depending on the access controls in place.