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Consider a critical multi-server system (the clients are not in scope for this discussion). Each server can be a physical machine or hosted as VM.

Is there any reason to believe that the physical setup would be more secure than the virtualized equivalent, with all things being equal (e.g. room configuration, sufficient hardware resources for both approaches, etc.)?

Is there any research to claim one or the other?

Edit: For further clarification (per requests in the comments), the question is primarily targeted at potential software exploits and networking vulnerabilities with regard to the traffic between the servers. For software exploits and vulnerabilities, consider those both on OS and the application level.

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    More secure against what? – a CVn Jul 5 at 8:20
  • All things being equal: Installing a hypervisor on a physical server and then running your OS and application in a VM is not inherently more "secure" or more insecure than installing the OS and application directly on the that same physical server. Typically though you won't do such one-on-one virtualisation and the VM will be on a shared platform with different and additional security trade-offs, complexity and benefits and delegation of control. – HBruijn Jul 5 at 8:54
  • More secure against what ? It can be considered more secure against malfunction and against high downtime and less secure in the case of security exploits/vulnerabilities. It also is more secure if the guest OS is damaged, you can still access it via host. – Overmind Jul 5 at 8:56
  • @HBruijn That is true, the VMs will be on a shared platform. However, the platform will host exclusively machines within the same security zone. And those "dditional security trade-offs, complexity and benefits and delegation of control" are what the question is about. – user3209815 Jul 5 at 9:27
  • @Overmind I've tried to narrow down my interest in the edit. "less secure in the case of security exploits/vulnerabilities" is what I'm primary curious about. – user3209815 Jul 5 at 9:28
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It really depends on what is on the scope of "security".

  1. If service availability is part of security, then usually, virtualized system are better on this topic because of:

    • the inherent mitigation of hardware fault.
    • Ability to take snapshot, etc... to ease backups and rollback
  2. If availability isn't on scope, then i would tell that, for sure, physical server are more secure since you remove a whole layer (the hypervisor one) that could bring breaches or vulnerability.

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largest additional risk from a vm are the memory timing attacks of one vm can likely potentially be used to read memory from another. Spectre and Meltdown spring to mind. https://www.theregister.co.uk/2018/01/02/intel_cpu_design_flaw/ for example

Yes this can likely be mitigated, but at a performance penalty. Hypervisor security is not trivial. Obviously such exploits can be used between processes on the same machine as well.

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The main differences that come to mind has to do with protection of critical data leakage.

With a fully encrypted physical server, temporary memory swap space would typically use encrypted swap.

While a virtual server could be defined as fully encrypted with its own encrypted swap, it's also subject to the host system memory management and swaps outside of the client VM. Depending upon the host system used, this host level buffer and swap may not be encrypted. Depending upon setup and criteria, this could range from unimportant to critical.

Access to the host gives unrestricted access to all running client VMs verses needing individual accesses for each physical server. I emphasize running because encryption is irrelevant when the system is running.

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