The application implements an up- and downvote function which alters a value within a JSON file. The POST parameters are not filtered properly and therefore an arbitrary file can be overwritten. The file can be controlled by an authenticated attacker, the content cannot be controlled. It is possible to overwrite all files for which the webserver has write access. It is required to supply a relative path (path traversal).
Solution:
The product allows user input to control or influence paths or file names that are used in filesystem operations.