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I just downloaded a disk image. After trying to install in a Virtualbox VM and seeing that it wasn't successfully booting into an installer, I checked into the md5sum. It seems the md5sum that is said online differs from my downloaded version. In fact, there are a variety of mirrors with a variety of recorded md5sum values. If it is the case that I downloaded a malicious disk image, can it have done any harm to my host OS from my VM?

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Whilst there is some isolation from the host, your VirtualBox VM may well have established network connectivity on your local network, which may have exposed your local devices e.g. unsecured file shares or insecure router with vulnerabilities or which uses default credentials.

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Short answer: nobody can guess.

It really depends on how you have configured you client VM, and what the malicious disk targetted. If it was simply a modified OS version that installs some malware on its partition that expects to be run on next boot, you are fine.

If it tried to collect some information and send it to a malicious server, things become worse, because the VM can get some information from the host, and it is normally immediately given a functional network interface. Here it really depends on what VMWare (or whatever hypervisor you used) has presented to its guest VM.

If is is a malware that directly targetted the VMWare virtualization system (i.e. is programmed to look to check if it is in a VM environment), anything can happen (depending on what the malicious program is designed to do) and you should thoroughly check what might have been changed in your host system (and network). Further references on that can be found on wikipedia

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  • @CaffeineAddiction: thank for the link! I've included it in my post. Jan 5 '17 at 12:35
  • @SergeBallesta What do you mean by "thoroughly check what might have been changed in your host system (and network)"? What steps should I take?
    – Rohan
    Jan 6 '17 at 0:13
  • To properly assess this situation we need to know the value of the target. VM escape, while possible, is a sophisticated attack that has to be targeted at the specific setup. Is it possible that this is the final stage of a sophisticated multi-step attack? Yes. Is it probable? Not likely. So lets not panic Rohan into wiping his home media and cat pictures server because he downloaded and run bad image. Jan 6 '17 at 15:54
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If executed or installed, then it's possible for malware to have broken out of the secure container that your VM hdd creates. However, in most cases, it's only your vm that's going to be infected and your system (with a little luck) should be fine.

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There are exploits one can use to break out of the VM container and gain access to the host. Most of the exploits I am aware of do this through the native 3D graphics functionality. So how much to worry depends on whether native 3D was enabled for this VM. It is not enabled by default, so the OP would have had to specify to enable. Oracle lists this feature as potentially insecure.

I'd also worry if installing the VM involved running any type of script. If so, I'd review the script to determine what it actually did.

Otherwise, I don't think you have too much to worry about. Of course, I assume you shut down the VM and removed it.

https://www.virtualbox.org/manual/ch13.html

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