This question notes that a person briefly connected an Android device to an Apple computer via USB, and one comment indicates that it would "quite possibly" be a risk:

In theory, yes, in practice, probably not. If it had been a Firewire device, quite possibly. – Matthew

Why is Firewire a bigger threat than USB? How can connecting a Firewire device to a machine be a security risk?

I am a PC user and don't know anything about Firewire.

  • This question is rather silly. In what case of a person having direct physical access to a machine would you expect security? Give me physical access to a server and there are a 100 ways to break in, most of them not taking much tech knowledge.
    – blankip
    Jun 10 '16 at 19:48
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    It's not a silly question -- why would I think that plugging my laptop into someone else's thunderbolt display could give them any privileged access to my computer? It's not like I handed it over to them and they took it into a back room to open it up and gain access, and I'm not running any software they gave me -- the laptop never left my hands, I'm just using a monitor.
    – Johnny
    Jun 10 '16 at 20:07
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    @LittleCode so, you should buy all your equipment (including keyboards, screens, printers...), unpack it from the sealed boxes, transport it wherever you go, and keep it under biometric padlocks when you aren't there? Unless you are holding military grade secret information in a room full of enemy spies, most physical actions are still safe, and it is good to know which ones may not be.
    – Davidmh
    Jun 11 '16 at 13:45
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    @LittleCode but it's such an inconspicuous situation: hey Little, my phone's nearly empty, mind if I recharge it from your computer? Joe Average wouldn't let a stranger do this, but he would not suspect a security risk from a person he knows. Jun 11 '16 at 19:13
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    @LittleCode: While your personal and private security measures seem to be formidable, that does not render moot the question the OP brought up. There are plenty of people out there who have no clue whatsoever about USB or Firewire vulnerabilities. Asking a question on how/why these are dangerous is exactly what this Stack is for, and it seems this is also a topic which many people here are interested in.
    – fgysin
    Jun 28 '16 at 15:10

Firewire and also Thunderbolt provide direct access to the OS memory, thus bypassing the operating system. See Wikipedia: DMA attack for more details on the possible attacks.

USB does not provide this kind of direct access. But it has other problems like the ability to unexpectedly emulate devices like a keyboard, see BadUSB.

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    Craziness. Who thought that was a good idea ;)
    – Desthro
    Jun 10 '16 at 15:26
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    @Cubic: The FireWire thing is also a natural consequence of how FireWire works: It's built to be fast. Capital F Fast. Which it is. The same with Thunderbolt. And at the point where someone can connect a compromised device to your computer, you've already lost; because they have physical access either to your computer or your device, which is a total loss. Jun 10 '16 at 16:38
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    The direct memory access is all the more frightening when you consider that Firewire has a peer-to-peer architecture, in contrast to USB, in which a host controls the devices. Jun 10 '16 at 17:16
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    @WillihamTotland - unfortunately, Joe Average user may have an infected/corrupted device, not know it, and plug it into his personal machine, thus infecting his own machine. It's not necessarily that a bad guy has gotten access to the machine and is plugging in his bad guy device.
    – FreeMan
    Jun 10 '16 at 17:51
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    @WillihamTotland: Interestingly, the original PC with its original keyboard connector could be taken over by a device plugged into the keyboard connector even before it performed its horribly slow RAM test.
    – supercat
    Jun 10 '16 at 17:59

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