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If one has a USB stick, originally from a trusted source and without hacked firmware, but one has used this USB stick with an unsafe system, then can it safely be plugged it into a Tails OS system and be overwritten by cloning Tails onto it?

By "safe", I mean that the system does not get physically comprimised (e.g. altered firmware) and the Tails OS is not modified.

If it's not safe, then what would a potential attack vector be?

Further Explanation

Of course one could just throw out the USB stick and buy a new one.

But a variation on this question would be plugging in the used USB in order to copy non-executable files from the unsafe system, and then asking if this is a safe way to transfer files?

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  • Safe from what? What bad thing do you not want to happen?
    – schroeder ♦
    Commented Dec 5, 2021 at 9:02
  • What kind of USB device are you speaking about?
    – F. Hauri - Give Up GitHub
    Commented Dec 5, 2021 at 9:24
  • Instead of cloning USB storage, you could simply dowload image from official site, then burn your owjn device with this image (after checking them).
    – F. Hauri - Give Up GitHub
    Commented Dec 5, 2021 at 10:37
  • Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.
    – Community Bot
    Commented Dec 5, 2021 at 12:05
  • OP, are you asking: Can the USB drive that contains the unsafe system possibly compromise the Tails instance on the system that the USB drive is connected to - and If so then, when Tails clones itself to the USB drive, could the Tails instance on the USB drive also be compromised as well?
    – mti2935
    Commented Dec 5, 2021 at 15:16

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No, it is not unconditionally safe.

If the USB stick is vulnerable to BadUSB type attacks, and if the "unsafe" system it has been used with was compromised to perform that kind of attack on connected USB sticks, then the firmware of the stick could be compromised to perform USB-based attacks on any systems it may be connected to in the future. This kind of compromise will not be removed by just overwriting the data on the stick, for example with a Tails image.

So after cloning Tails onto it, such a stick would still (try to) attack any system it is plugged into. To begin with, it may compromise the very system you use to do the cloning. It may also attack the installed OS of systems you intend to boot Tails on, if you plug it in while the installed OS is running. And it may even try to attack the Tails image as soon as you boot it from the stick. (Although Tails is certainly not the easiest of targets.)

Whether any of these attacks will actually succeed is a different question. But they are theoretically possible.

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    Imho BadUSB was overhyped by the media and not a lot of controllers in the flash drives are vulnerable to it.
    – Sir Muffington
    Commented Dec 5, 2021 at 18:24
  • 1
    Definitely. Hence my two emphasized ifs. But it is theoretically possible, so the absolute question "is it safe" must be answered: "No, not absolutely."
    – Tilman Schmidt
    Commented Dec 5, 2021 at 18:35
  • OK, so just inserting a USB stick into a compromised system could possibly turn it into a BadUSB, for example? I ask, because the one tutorial I found online on creating a BadUSB involved opening up the USB stick and shorting two pins.
    – hsjpB
    Commented Dec 5, 2021 at 18:44
  • Just inserting a vulnerable USB stick could do that, yes. The BadUSB PoC published by Adam Caudill und Brandon Wilson in 2014 worked against unmodified sticks with a certain type of controller. One would hope that controller manufacturers have since elliminated that kind of vulnerability, so as @SirMuffington wrote, sticks vulnerable to BadUSB should be rare.
    – Tilman Schmidt
    Commented Dec 5, 2021 at 18:59
  • I understand now, as far as BadUSB goes. But it is still possible that there are newer BadUSB variants that could comprimise the USB firmware even on a newer stick? Or are you saying that it is possible to eliminate this type of attack completely with a properly manufactured controller?
    – hsjpB
    Commented Dec 5, 2021 at 19:08

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