It is an important and little-known property of web browsers that one document can always navigate other, non-same-origin windows to arbitrary URLs. Perhaps more interestingly, you can also navigate third-party documents to resources served with Content-Disposition: attachment, in which case, you get the original contents of the address bar, plus a rogue download prompt attached to an unsuspecting page that never wanted you to download that file. Proof of concept code included.
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