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Security Risks of VirtualBox Shared Folders

What’s the actual (real, demonstrable) risk of shared folders in VirtualBox - this should be stated clearly in an Intro section to the VirtualBox Guest Additions page.

Yes, it weakens isolation between host and guest, but what is the realistic attack angle? Guesses:

  • You run some dodgy executable in the VM and it accesses your host with root permissions or inserts malware there?

  • Doesn’t it still have to break out of/breach hypervisor sandbox (they use some unidentified bug to escalate privileges)?

  • Attacker inserts a malicious file and does some social engineering such as replacing the file in that folder with one that looks similar that is malware (which is later shifted to the host)?

  • Copy/paste buffer and keyboard/mouse shared memory etc allow access to the host, meaning if the VM is rooted they can trivially hack your host?

  • General exploits over data channels and shared memory?

  • Attacker uses an escalation bug when having local but unprivileged access to a host to execute arbitrary code within the Linux kernel to gain complete control over the system?

  • Abuses the symlink functionality somehow?

  • All of the above?

    https://www.virtualbox.org/manual/ch04.html#sharedfolders doesn’t mention any major security issues there.

Can’t find any solid references re: security risk, just low quality guesstimates like this:

https://www.reddit.com/r/linux/comments/1k6biq/safety_of_virtualbox_with_shared_folders/

https://security.stackexchange.com/questions/88684/how-secure-is-virtualbox-for-privacy-anonymity

https://serverfault.com/questions/59346/virtualbox-guest-additions-security-issues

And at the moment, we just state in the wiki this functionality is “unrecommended”. TAILS is also vague on the issue (if running TAILS inside VirtualBox), they just say:

https://tails.boum.org/doc/advanced_topics/virtualization/virtualbox/index.en.html

With the shared folders feature of VirtualBox you can access files of your host system from within the guest system.

Make sure to understand the security implications of ?accessing internal hard disks from Tails before using this feature.

Well if that’s the case, then it should be backed up with something solid e.g. CVE references, or some expert bagging out VirtualBox re: their screwing up this functionality badly somehow which poses serious risks.

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Right. It’s a weak argument “as few features as possible”, “use as few code paths as possible”. Currently we state:

Shared folders are also discouraged because it weakens isolation between the guest and the host. Providing a mechanism to access files of the host system from within the guest system via a specially defined path necessarily enlarges the attack surface and provides a potential pathway for malicious actors to compromise the host.

But the same could be said about any virtualizer. Perhaps to a less degree because the virtualizer itself is considered more secure but then I wouldn’t know why it would still be a good idea to pick on that feature specifically. If you could clarify that in the wiki, that would be good.

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Fixed.

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