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If an attacker were to set up a netcat listener (nc -lvnp 4444), then is it possible to take control of their device using that listener? Whenever I look for an answer online, all I can find is how to setup your own reverse shell with netcat and never anything on exploiting an attackers reverse shell.

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No. All their listener is doing is writing to standard output (and in the other direction, carrying the attacker's standard input to your machine). In particular, it's not writing commands into a shell on the attacker's machine, or anything like that. There's no software on the attacker's side that is treating anything coming down that connection as an instruction, so no, you can't "take control of their machine". You could, I suppose, write false stuff into their listener to try and scare or confuse them, or you could send a lot of bell characters and try to annoy the heck out of them, but that's about it.

Also, generally they are only going to listen for one connection at a time, so you'd have to find their listener before they use it. If the attacker is being careful, they'll have a firewall and only have opened inbound traffic to the listener from the IP range that they're attacking, so you can't even necessarily use this to attack attackers who are attacking somebody else. Finally, in the scenario you're describing where they've set up the listener because they are setting up a reverse shell on you, you have MUCH bigger problems (specifically, the attacker already has arbitrary code execution on your machine and is about to take real-time remote control of it).

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"If an attacker were to set up a netcat listener (nc -lvnp 4444), then is it possible to take control of their device using that listener?"

Not per se. netcat has not this capacity (obviously: otherwise, we'd all steer clear from it).

It is theoretically possible that netcat might have an undisclosed vulnerability, or at least your attacker's copy might have an intentionally built backdoor, so that such control would be possible.

(And there are some attacks (denials of service, mostly) at the TCP level that would work on a un-hardened machine as long as they had at least one open (listening) port. The probability of this being the case is also really low).

At the same time, however, you'd also have to defend from the shell netcat has been connected to.

So, in this scenario, to hoist the attacker on their own petard, you'd need:

  • a fake (sandboxed, virtualized, emulated) system vulnerability that the attacker believes they're exploiting, to get them to fire their netcat listener without actually getting in control of your system,
  • a fake (or vulnerable) copy of netcat on the attacker's machine
  • evidently, a not too skilled or experienced attacker

Given all the above, the answer is yes.

But I believe you can see for yourself the low probability of this scenario (unless the attacker had been carefully set up - in essence, social engineered into attacking; rather than attack, this would be a sting operation), I'd say that the answer ought to be no.

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