I realized that the __came_from and __redirect_to url parameters I added to handle issues with the LoginAction and NewItemAction could be used for XSS or other purposes. So I check them using a new clean_url(url) function. This tries to validate that the url is under the tracker's base url and that the components of the url are properly url encoded. If it thinks something is wrong with the url, it will raise a ValueError. I decided to not attempt to fix the url's if there is an issue, better to bring it to the tracker admin's attention. Changed the code paths in NewItemAction and LoginAction that deal with the form parameters to use the clean_url function on the form input first.