Authcache vulnerabilities? In my experience Authcache gives a great enhancement to performance, however I am wondering what are the potential vulnerabilities using authcache and boost together? My worry is that when the administrator does not exclude user specific paths in boost configs, a saavy user can somehow access to other users' cookies and do nasty things. 

I guess it is not just a hypothesis, as I've seen that at least in one occasion in a boost+authcache+varnish arrangement a user reported that others have sent message on her part without her knowledge. If this indicate a real security hole, how should one counter int? Which paths should be absolutely excluded from being cached by boost?

What other potential security holes can be in this setting and how to avoid them?
Long term I would take a look at ESI over authcache. Not sure when manarth will get a stable release of 7.x out. ESI has fairly strong security with rotating keys and things like that.