openHAB, a provider of open-source home automation software, has add-ons including the visualization add-on CometVisu. Prior to version 4.2.1, CometVisu's file system endpoints don't require authentication and additionally the endpoint to update an existing file is susceptible to path traversal. This makes it possible for an attacker to overwrite existing files on the openHAB instance. If the overwritten file is a shell script that is executed at a later time, this vulnerability can allow remote code execution by an attacker. Users should upgrade to version 4.2.1 to receive a patch.