Lots of sensitive information leaks in the Referer header. This paper has a bunch of scary examples:
I'm not sure whether we can scrub the Referer header by default because lots of folks use the Referer header for all kinds of crazy stuff, but we should at least give sites an easy hook for scrubbing it. There probably should be a couple options:
1) Remove header entirely.
2) Strip down the Referer to just the origin.
Maybe in a future version of CSP.