Evil pixels: researcher demos data-theft over screen-share protocols

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Users see white noise, attackers see whatever they just stole from you

Pen Test Partners' data-stealing screen

Do not ajust your screen: there’s data in this noise

It’s the kind of thinking you expect from someone who lives in a volcano lair: exfiltrating data from remote screen pixel values.

The idea comes from Pen Test Partners’ Alan Monie, taking a break from sex toy hacks and wondering how to get data over a connection like RDP (remote desktop protocol) when the target had blocked file transfer (or the target is using a VMware console that can’t transfer files).

His approach: since the point of a remote desktop is that it’s the contents of a victim’s user’s screen that gets copied over the wire, encode the data you want to steal into the screen data, by flashing up a screen full of what looks like white noise.

Monie’s PTP-RAT proof-of-concept code to do this zips down to a mere 13 KB. At that size, a skilled attacker could upload during an RDP session without attracting attention.

The only stumbling block Monie had to deal with to create it is compression: RDP didn’t transmit screen colour data completely accurately.

However, restricting the exfiltration encoding rate to three bits per pixel (encoding just one bit on each of the Red, Green and Blue values) took care of the compression issue, allowing him to pull a 3 MB file off the target in “a few seconds”.

Here’s how PTP-RAT functions, pretty much in full:

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As far as Vulture South can tell from Monie’s video, the victim won’t see the alteration – because that’s what’s sent over the wire to the attacker, and they’re expecting to see the screen flashes. ®

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