Piano LED Visualizer is software that allows LED lights to light up as a person plays a piano connected to a computer. Version 1.3 and prior are vulnerable to a path traversal attack. The os.path.join call is unsafe for use with untrusted input. When the os.path.join call encounters an absolute path, it ignores all the parameters it has encountered till that point and starts working with the new absolute path. Since the “malicious” parameter represents an absolute path, the result of os.path.join ignores the static directory completely. Hence, untrusted input is passed via the os.path.join call to flask.send_file can lead to path traversal attacks. A patch with a fix is available on the master branch of the GitHub repository. This can also be fixed by preventing flow of untrusted data to the vulnerable send_file function. In case the application logic necessiates this behaviour, one can either use the flask.safe_join to join untrusted paths or replace flask.send_file calls with flask.send_from_directory calls.