You are advices to set configure the following setting in Tor Browser in Whonix:
Edit → Preferences → Applications ->Portable Document Format (PDF) → Save File
You are advices to update as soon as updates are available. This blog post will be updated as new information come in.
(Do that same with Firefox / Iceweasel if you are using that elsewhere.)
Problem description at Mozilla Firefox blog:
Impact in Whonix:
– Unless you were using AppArmor, local files within the VM would be accessible.
Tor Browser upstream Bug report:
Whonix forum discussion: