Another reason to block fonts at the proxy
Last week Apple released a bunch of patches up and down its product line. One of the vulnerabilities it fixed in OS X was a vulnerability in its font parser.
In the past you could mitigate vulnerabilities like this by only installing fonts from trusted sources, but since it’s now possible for web pages to transmit fonts along with other content, there’s a limitless number of untrusted fonts out there in the world.
Since it may take a while for all of the major operating systems to shake out all of the problems in their font subsystems, that’s the reason I’ve recommended filtering fonts at the proxy.