Security considerations for USB keyboard/mouse switches

Question

I am considering purchasing a basic USB keyboard/mouse switching box in order to allow me to use the same keyboard and mouse with two different physical machines. This is similar to a KVM (keyboard video mouse) switch, but just for the input devices rather than the display as well.

The two devices I want to switch between are my highly secure main computer and a less-secure secondary laptop that I use for travel (hotel Wi-Fi, etc) and for browsing potentially insecure non-tech websites (eg: online furniture shopping, local businesses, etc).

The roles of these two machines are clearly separated, for example I do not log in to any valuable online services using the travel laptop, and I have a separate set of online accounts to use on it. I treat the machine as though it is definitely compromised.

I am aware that Belkin have a range of 'secure' switches that are NIAP listed and have passed various accreditations, however most of these are more expensive than consumer switches as they are designed primarily for business/government use.

One that stands out to me is the Belkin OmniView Secure Series: https://www.amazon.co.uk/dp/B000UNBNVW/, which has the following security features advertised:

• Listed by NIAP and pending NIAP Common Criteria validation to EAL 4
• Prevents data transfer between classified and unclassified computers
• Features no hot keys or OSD to prevent data from being stored on KVM Switch
• Non-reprogrammable firmware prevents tampering with KVM logic
• Provides full support for USB computers, keyboards, and mice

Are you just paying for the accreditation here or is there a legitimate security advantage over more basic consumer switches?

I know that using a USB switching box does not protect me from attacks against the peripherals themselves, such as a vulnerable keyboard controller, badusb, etc.

However, the bit that concerns me just by looking at the box is that there is a cable from both of my machines that connects to a central point. These machines are really supposed to be air-gapped from each other.

Are my security concerns valid/appropriate and do you think there is anything I have missed?

Could there also be a better solution to my problem?

Thank you.

Answer 1

Points on the product page

Are you just paying for the accreditation here or is there a legitimate security advantage over more basic consumer switches?

• Listed by NIAP and pending NIAP Common Criteria validation to EAL 4

  This is just the certification, although certification should check for some issues.

• Prevents data transfer between classified and unclassified computers

  As it is a KVM it means you can swap between using machines without having to change controls, but it doesn't prevent transfer, it just reduces the need to transfer files.

• Features no hot keys or OSD to prevent data from being stored on KVM Switch

  This may be of use, although a lot of shortcuts could be implemented without logging any data (only intercepting a set combo and not storing any input data)

• Non-reprogrammable firmware prevents tampering with KVM logic

  This is a double-edged sword, on one hand malware cannot be loaded onto the device, on the other any bugs in the device cannot be fixed.

• Provides full support for USB computers, keyboards, and mice

  Provides no extra security

Bridging the airgap

However, the bit that concerns me just by looking at the box is that there is a cable from both of my machines that connects to a central point. These machines are really supposed to be air-gapped from each other.

The KVM would be a path over the airgap, but you also need to consider other ways to bypass it, such as:

• Using load to signal over the power line voltage
• Using microphones and speakers to communicate using inaudible frequencies
• Using fan speed to transmit data

You have to weigh up any bridge over the airgap as:

(likelihood of attack + ease of defence) / necessity

In this case, if you need to use the same inputs you can treat it as an acceptable risk in the same way you would treat plugging both machines into the same power supply as an acceptable risk.