[Ongoing] Tainted data should be handled more carefully

[François Marier]

There are two types of data that Mahara manipulates directly: images and compressed files.

Images are resized using PHP libraries (running as the Apache user) and zip files / tarballs are uncompressed through PHP libraries (in the case of Leap) or through shelling out to run unzip.

The problem with this is that this untrusted user data could potentially contain exploits which would take over the web server process and potentially write to / delete the dataroot or the database.

Ideally, we should have the current insecure file manipulation mode for people on shared hosting or Windows as well as a more secure mode where tainted data is handled in a separate process and by an unprivileged and separate user account.