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I have told my users for years not to ever click on PDF Documents if they are not 100% sure they know where it came from as they can sometimes be the delivery vector for malicious code.

Recently, one of my users sent me a screenshot of an obvious scam email. They then proceeded to send me a screenshot of the PDF. I then asked them why they opened the PDF if they knew it was from a malicious source ... to which they answered "I didn't, I had google open it for me".

So, aside from the fact that this induces a /facepalm, and aside from the fact that "google doing it for you" simply means there is a javascript PDF viewer being run by your browser ...

Are there any known vulnerabilities that exploit google's PDF viewer? Is the google pdf viewer sandboxed in such a way that prevents it from accessing the rest of your google account?

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    Which of the various Google PDF viewers? The one on Google Drive renders the PDFs server-side and sends them to the browser as a PNG (overlaid with invisible text), so that would indeed seem to be a secure option. The PDF viewers integrated in Chrome/Firefox are effectively a sandboxed extension, so viewing an untrusted PDF would be no worse than viewing another untrusted website. The user might have a point that this is more secure than opening the file e.g. in Adobe Acrobat.
    – amon
    Jul 7, 2022 at 17:49
  • @amon do you know which of these viewers is used for gmail (both personal and profession)? Jul 7, 2022 at 18:46
  • also, do you have a source? Jul 7, 2022 at 18:47
  • Google is usually fast to fix critical bugs, so it is unlikely that there are currently publicly known but unfixed bugs. And we don't know about bugs which are not publicly known. That said, PDF viewers are complex and there were many bugs in the past including bugs in PDF readers from Google. So just because nothing is publicly known does not mean that there is no such (still unknown or at least not public) problem in the current product or will be in a future implementation of it. Jul 7, 2022 at 19:04
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    When they went with an open-source solution, they switched to an OEM PDF viewer called "pdfium"... it's made by Foxit Software (a Chinese company). There are always bugs in complex software...you can view some here: bugs.chromium.org/p/chromium/issues/list?q=pdfium&can=2 The source code for pdfium is here: pdfium.googlesource.com/pdfium/+/master Jul 7, 2022 at 19:13

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Google Chrome and Mozilla Firefox have had built-in PDF viewers for years. Maybe that's what you're talking about. I've not heard of any PDF related vulnerabilities in them for quite some time.

Any PDF reader may have vulnerabilities and these are two primary ways to be sure you won't be hacked when opening PDF files:

  • by opening them on a remote PC via any remote desktop software
  • by using an external service to convert them into an image file, e.g. PNG

Even using a Virtual Machine can be unsafe because every VM that I've ever known has been exploited enough to escape it and get Administrator/System level access on your host PC.

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  • "100% sure you won't be hacked" Famous last words... both methods you mentioned are not completely foolproof. Jul 8, 2022 at 2:02
  • @multithr3at3d I'm all years how you can possibly be hacked by either of them. At least a single accident over 40 years of computing will make me change my mind. Let's go! Jul 8, 2022 at 7:48
  • I think you meant "remote app isolation" instead of "remote desktop". Depending on how the remote desktop is configured, it can allow reverse traffic. Using RDP in this way is a "poor man's" attempt at remote app isolation. There has been no known way to defeat pure remote app isolation.
    – schroeder
    Jul 8, 2022 at 7:49
  • You're now trying to stretch Remote Desktop'ing to where I've never intended it to go. OK. This way indeed everything can be misconfigured and misused, however again I was talking about vulnerabilities not PEBKAC. In terms of vulnerabilities these two options are as safe as humanly possible. In the first one you basically get an image, in the second one you get e.g. PNG files. Jul 8, 2022 at 7:54
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    Your statement: "be 100% sure you won't be hacked when opening PDF files by opening them on a remote PC via any remote desktop software" -- that's far too undefined and too open to interpretation, and is not a PEBKAC issue. RDP on a remote PC with a vulnerability can most definitely reach back to the remote user.
    – schroeder
    Jul 8, 2022 at 7:56

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