On 2016-01-08 00:50:51 -0200, Rodrigo Menezes wrote: > Many of us have now been long aware of the possibility of > programming an USB device to emulate a keyboard and automatically > send keystrokes in order to perform malicious actions on a > computer. Some of the most interesting payloads that can be used > with this technique are based around downloading or creating an > executable file and then running it. > I'd like to bring to light that this attack could be combined > with DLL hijacking, with some benefits for the attacker. > For instance, a payload which simply downloads a DLL to the > current user's folder tends to complete faster and be more > reliable than one which tries to transfer an executable > AND immediately run it. The DLL would then most likely > be found and executed by a vulnerable installer [...] This way, > there would be no need for embeeding in the payload a complicated > attempt of bypassing the active defense mechanisms. Once you can fool the user to plug the USB device, you don't need anything else. The device may appear as 1. A mass storage, and 2. A keyboard or any other HID, and 3. Some unknown hardware Once the W-ndows enumerates this hardware, it will try to find and automatically install drivers for it. With a mass storage and a keyboard it will succeed, thus immediately bringing them to use, and unknown hardware would bring up a "search for drivers" dialog, where the attacker may (after some delay) send keystrokes to choose "search removable devices for drivers". Obviously, the mass storage part of the USB device would contain suitable .inf file pointing to malicious binaries. The USB device capable of performing such attack may be as simple as ATtiny85 + 25Q64 chips (both are available in a 3*4 mm SOP8), with a total cost of 1 EUR. The 25Q64 offers 8 Mbyte of storage, which is well enough for almost anything.
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