"Content-Disposition: attachment"
Summary:
We currently serve some files off the primary domain (with "Content-Disposition:
attachment" + a CSRF check) and some files off the alternate domain (without
either).
This is not sufficient, because some UAs (like the iPad) ignore
"Content-Disposition: attachment". So there's an attack that goes like this:
- Alice uploads xss.html
- Alice says to Bob "hey download this file on your iPad"
- Bob clicks "Download" on Phabricator on his iPad, gets XSS'd.
NOTE: This removes the CSRF check for downloading files. The check is nice to
have but only raises the barrier to entry slightly. Between iPad / sniffing /
flash bytecode attacks, single-domain installs are simply insecure. We could
restore the check at some point in conjunction with a derived authentication
cookie (i.e., a mini-session-token which is only useful for downloading files),
but that's a lot of complexity to drop all at once.
(Because files are now authenticated only by knowing the PHID and secret key,
this also fixes the "no profile pictures in public feed while logged out"
issue.)
Test Plan: Viewed, info'd, and downloaded files
Reviewers: btrahan, arice, alok
Reviewed By: arice
CC: aran, epriestley
Maniphest Tasks: T843
Differential Revision: https://secure.phabricator.com/D1608
549146bc7c