How To Isolate Virtual Machine From Host

Virtual machines are great tools for overcoming resource limitations to run multiple operating systems simultaneously while keeping them separate from each other. However, the virtual machine and the host share many hardware and software resources, leading to extensive interaction between the two machines. Is it possible to isolate them completely?

You can’t completely isolate a virtual machine from the host because the guest relies on the host’s NIC, memory, and other physical resources to function. However, you can minimize the interaction between the two machines by restricting the data flow between the host and the VM via host settings.

Different hypervisors offer varying degrees of isolation. Read on to learn how to maximize isolation on popular hypervisors. I’ll also recommend alternatives to isolation.

How to isolate virtual machine from host.

How to Isolate Virtual Machine From Host

As mentioned earlier, it’s not possible to completely isolate a VM. However, you can restrict the amount of data exchanged between the machines. The available options to implement such restrictions depend on your virtualization software.

Some virtualization software allows restrictions on copy/paste and drag and drop to minimize the data flow between the host and the VM as well as between multiple VMs on the same physical machine. 

Other virtualization software, such as Parallels Workstation, has a straightforward process of isolating the guest. All you need to do is select the virtual machine you want to isolate and select the Isolate option under Configure > Options > Security. However, other tools may have different isolation settings. 

Below, we’ll discuss the isolation features offered by the two most popular virtualization platforms for regular users. 

Isolating Your Virtual Machine When Using VMWare 

VMWare is one of the most popular VM tools and allows you to restrict file transfer between the host and the guest. However, this option is not available for remote virtual machines. 

Regardless of the software version, you can enable or disable two options:

  • Drag and Drop. This option disables transferring files between the host and guest systems.
  • Copy and Paste. This option enables and disables copying and pasting files or text from the host system to the VM and vice versa. It also controls the copying and pasting of files from one virtual machine to another.

Since these options are enabled by default in VMWare, you need to disable them via the settings pane. And as they’re guest isolation options, you can access them only if you’ve installed VMWare on the guest operating system.

To access these settings:

  1. Open VMWare and select the target virtual machine. 
  2. Select Settings and click Configuration. You’ll see the “Drag and Drop” and “Copy and Paste” options.
  3. Disable them by removing the check mark next to each option.

Isolating Your Virtual Machine When Using VirtualBox

Another commonly used tool for creating virtual machines is Oracle’s VirtualBox. Fortunately, the options for transferring files between the virtual machine and the host and copy/paste options are disabled by default in VirtualBox. 

As a result, you’ll get better VM isolation out of the box compared to VMWare. However, if you’re not sure whether these options are enabled, you can check through the following steps:

  1. Go to the window of the currently running virtual machine and select the Device menu.
  2. Locate the Drag and Drop option and expand it. You’ll see four menu options, namely Disabled, Host To Guest, Guest To Host, and Bidirectional. 
  3. Check Disabled to isolate your VM from the host.

To enable file sharing and copy-paste options in VirtualBox, you must specify paths and folders to give the VM access to a file or folder. These features give VirtualBox VMs a good level of isolation from the host.

You Can Isolate Your Virtual Machine’s Internet Connection

In many cases, users aren’t worried about sharing files between the host and the VM. Instead, they have security concerns about malicious attacks or viruses leaking from the host to the guest and vice versa. 

This problem stems from the fact that the host channels the internet connection to the guest, functioning like a router. As a result, whatever threat attacks the host can also threaten the virtual machine.

Nearly all virtual machines use Network Address Translation (NAT) as their default networking mode. NAT is the same method used in routers, mapping the guest’s IP address to the host’s IP address. 

The VM software places a NAT firewall between the host and the guest to provide higher security. However, the virtual machine has the same access privileges as the host.

Most VM tools, including VirtualBox and VMWare, offer different connection types to match your networking needs. Apart from NAT, the most common types are the following:

  • Bridged. Your guest machine is directly connected to the host’s network adaptor, so the host doesn’t route the connection.
  • Internal network. With this mode, you can build an internal network consisting only of virtual machines. They’re fully isolated from other devices and the host, making this mode more secure than the Bridged mode.
  • Host-only. As the name suggests, the virtual machine can only connect to the host machine. You can also add other virtual machines and create an internal network to communicate only with the host.

As mentioned, these are the most common network modes found on most VM tools. However, you may find other modes on specific tools. For example, VirtualBox has UDP Tunnel, Virtual Distributed Ethernet (VDE), and Cloud networking modes, each applicable to certain purposes.

Despite these options, if you want full isolation, you need a separate physical NIC to dedicate to your VM. For example, you can connect the virtual machine directly to an ethernet connection and connect your host machine via WiFi. 

In such cases, you need to completely disconnect the host from the guest by choosing the right option in your VM software. For example, VirtualBox’s Not Attached option disconnects the VM from the host machine. Then, you can connect it directly to another Network adaptor identified in the VM tool’s network settings. For VMWare, you can follow the steps described here.

Benefits of Isolating Your Virtual Machine  

Isolating a VM from a host means eliminating or restricting the ways in which the two machines can interact. If successful, the machines can’t share folders, files, or applications. 

In addition, if you have other devices connected to the same network as the guest and host machines, the virtual machine will be isolated from them. 

Isolation can be beneficial in the following ways.

Isolation Results in Higher Security for the Host and Guest 

The most important benefit of isolating machines is security. Although a virtual machine is self-contained and isolated from the host, these machines still have some level of interaction because they use the same physical resources. 

As a result, your machines will be prone to each other’s security threats. For example, if a file or application on one machine is infected, it can compromise the other in some situations.

Isolation Reduces the Likelihood of Mistakes 

Virtualization can increase the likelihood of mistakes because both machines run on the same physical stack, and files can be transferred between them. 

An action on one machine may affect the other. For example, suppose you use your virtual machine to experiment with different viruses or security threats. A powerful antivirus installed on your host device can detect any virus that enters your virtual machine. 

Moreover, sharing files between the host and guest machines increases the chances of errors. For example, you may accidentally delete folders from a machine you were not supposed to.

Isolating Resources Ensures Availability and Keeps Performance Up 

One of the most significant problems with virtualization is that the host and the guest have to share the same resources. As a result, one machine can hog the resources and lower the performance of the other if they run simultaneously. 

There are different isolation solutions to this problem. For example, you can dedicate specific CPU cores to the virtual machine so it doesn’t have to share processing power with the host or other VMs. 

Or, if your virtual machine requires a faster internet connection, you can dedicate specific network adapters to it.

Containers vs Virtual Machines

One of the popular alternatives to virtualization is containerization. It involves using specific software tools, called containers, to virtualize resources and isolate specific environments from physical servers or other infrastructure. 

In this sense, virtual machines and containers serve the same purpose. However, they have key differences that make them suitable for different purposes. Here’s how they differ:

Containers Are Lighter Than Virtual Machines 

The most significant difference between containers and virtual machines is what they virtualize. Virtual machines virtualize the entire computer system, including the hardware. On the other hand, virtual containers start virtualization at a higher level: the operating system. 

This key feature has made containerization a more popular alternative to virtual machines.

A container is much lighter than a VM because it only needs the contained application and shares other libraries and binaries. In contrast, a virtual machine carries the guest OS and its kernel in addition to libraries and binaries.

Containers Provide Weaker Isolation Than Virtual Machines 

Since container virtualization starts above the OS level, a container will share many resources with its host. As a result, containerization provides weaker isolation from neighboring environments. 

Virtual machines only share hardware with the host machine, so there’s a lower chance of interaction between the host and the guest. Weaker isolation creates more security concerns and calls for more robust security measures.

You Can Do More With Virtual Machines Than With Containers 

Containers share the operating system with the host. This restricts the number of tasks you can perform with your machine. 

For starters, you’re stuck with only one operating system because it’s shared. So, you can’t do tasks that require multiple operating systems. Plus, containers have fewer resources than virtual machines. Therefore, you can’t perform heavy and resource-intensive tasks on them.

Maximizing Security in Virtual Machines

Although isolating the virtual machine is one of the best ways to address security issues, it’s not enough because full isolation is impossible. As a result, you need to take extra measures to ensure the highest level of security. Here’s what you can do:

Use a Secure Hypervisor

There are different virtualization software with varying security levels and options. You may not be able to find a hypervisor that’s 100 percent secure because software tools inevitably have vulnerabilities. 

However, it’s essential to do your homework and choose a more reliable platform that matches your needs.

Keep Everything Updated

If you’re worried about malware infections, you should have robust security options to protect your machines. Not only do you need a powerful antivirus, but you must always keep it updated to get the highest level of protection.

However, not every malware can be detected by antiviruses. Some are specifically designed to exploit vulnerabilities in hypervisors. One of the best ways to ward off these threats is to update your virtualization software regularly.

Practice Cyber Security Best Practices

Internet security isn’t limited to virtual machines; every general user is advised to avoid actions that put their computers at risk of attacks and infections. So, you should also practice internet hygiene, especially if you connect to the internet on your virtual machine. 

If you acquire a file from an unknown source, the recommended approach is to open it on an isolated VM. This way, even if the file is infected, your main OS will likely stay unharmed. 

Be Careful 

When you run multiple host and guest machines, it’s easy to mix things up and create disasters. For example, you may forget that you have shared a specific file on both machines and lose it to a malware infection. Or you may insert an infected flash drive into a USB port that automatically passes through to your VM. 

Final Thoughts

Isolating a virtual machine from the host is a great security measure for developers and security experts.

However, achieving complete isolation is nearly impossible because the two machines share many resources. Still, you can restrict some actions, such as drag-and-drop and file sharing, to minimize data transfer between the two machines. 

An alternative approach is to use a container, which applies virtualization to your OS rather than at the hardware level. However, your containers will have more limited resources compared to a VM.