Link Previews and You
5 points by JadedBlueEyes
5 points by JadedBlueEyes
I found this quite interesting: a deceivingly simple feature with far-reaching privacy implications.
A related issue I've been pondering is images in e-mails. Most modern clients ("user agents") will not blindly request an image from your machine. Webmail is another story. Take GMail, for example: it displays images by proxying them through Google's cache, and will often do so unprompted. This seems good on the surface - the client does the obvious thing (just display the HTML), and the user's browser is not really involved in external requests.
On the other hand, this still discloses several facts about the recipient: namely, that they opened the message at a given time. You might be excused for thinking "the attacker only gets one shot", but no - from my testing, the proxy respects the cache headers, so as to enable useless gimmicks important marketing features such as countdown GIFs generated on-demand (these usually contain just 60 frames for the next minute). So, if you repeatedly open the same e-mail, several requests have to go out from somewhere, and they are not temporally de-correlated.
I'd rather stick with "Show images" on demand, thank you.
Yeah! Often "obvious" features have pretty far reaching implications, I know the email image trick is used by both marketers and spammers to identify which inboxes are being read
Good read. This is why my IRC client project comes with a separate service for generating link and media previews. It's a privacy and security problem with essentially all other IRC clients that have link preview support, that the IRC client itself is fetching the link or media, exposing your connection to people with malicious intent. On top of that, it's good to have your link preview fetcher isolated from the rest of the application server, so a malicious link doesn't have access to your users data if something bad does get through. Oh, and then there's DNS rebinding attacks, too! With a cache in place, a multi-user IRC client also somewhat masks the 'you know who saw the link' issue mentioned in this thread, as any number of users on your instance could be the one who saw the link and no one knows how many users you have. Though I guess this breaks down with private messages.
Kind of one of those things a lot of people don't seem to think about. Sorry, I guess I am just patting myself on the back in this comment, but this topic really interests me and my first time seeing something on Lobsters that is really in my wheelhouse, so I had to say something. :)