The Google Photos picker of the upload page fetches the thumbnails of the picked images through the server, with the access token of the Google Photos account. The task took the address to fetch from the request without checking it and asked for no form token. A prepared page on another web site could therefore make the server send the access token of the account to any address, or fetch addresses inside the network of the server, in the name of a logged in administrator; a back-end user with the permission Manage could do the same directly. The token is valid for about an hour and reaches what the picker session of the account reaches.