A while back, I wrote an article about Malduino, an Arduino-based, open-source BadUSB device. I found the project interesting so I signed up for an Elite version and sure enough, the friendly postman dropped it off in my mail box last Friday, which means I got to play around with it over the weekend. For those who missed the article, Malduino is USB device which is able to emulate a keyboard and inject keystrokes, among other things. When in a proper casing, it will just look like a USB flash drive. It’s like those things you see in the movies where a guy plugs in a device and it auto hacks the computer. It ships in two versions, Lite and Elite, both based on the ATmega32U4.

The Lite version is really small, besides the USB connector it only contains a switch, which allows the user to choose between running and programming mode, and a LED, which indicates when the script has finished running.

The Elite version is bigger, comes with a Micro-SD card reader and four DIP switches, which allow the user to choose which script to run from the card. It also has the LED, which indicates when a script has finished to run. This allows the user to burn the firmware only once and then program the keystroke injection scripts that stored in the Micro-SD card, in contrast to the Lite version which needs to be flashed each time a user wants to run a different script.

These are the two Malduinos and because they are programmed straight from the Arduino IDE, every feature I just mentioned can be re-programmed, re-purposed or dropped all together. You can buy one and just choose to use it like a ‘normal’ Arduino, although there are not a lot of pins to play around with. This freedom was one the first things I liked about it and actually drove me to participate in the crowd-funding campaign. Read on for the full review.

The Hardware

So the Elite board arrived as schedule and I found myself some time to look an it. Despite being longer than the Lite version, it’s still quite small, measuring roughly 4.6 cm x 1.1 cm (around 1.8 in x 0.43 in), which you can easily adapt to an old USB case, although you’ll have to cut some holes for the DIP switches and the Micro-SD card. In the crowd-funding campaign, the original sketch was for a 3 DIP switch version but the final Elite has four, which I found nice. I plugged it in to an old computer, after some consideration about which firmware it could ship with and what it could do to my laptop, and sure enough a red LED appeared. And that was it. Nothing else.

After playing around with the switches and exercising some RTFM, I realised that the firmware it ships with is probably some sort of Q.C. test for the dips, which makes the Malduino output the numbers 1 to 4 (actually simulating a keypress 1 to 4), depending on which switches are ON. So far so good, it works and I’ve seen worse PCB boards than this one. The board has holes for six pins, which I did not trace to the micro-controller and I don’t know what they are for.

The Setup

Setting up the Malduino requires that you have the Arduino IDE installed and up to date. You’ll need to open up the board manager and install the Sparkfun boards since the Elite is programmed as a ‘Sparkfun Pro Micro’ running at 3.3 V and 8 MHz. Then you need to go the Malduino Script Converter website which serves several purposes:

• It allows to convert scripts between the Lite and Elite versions
• It allows you to choose your keyboard layout language
• It auto generates the Arduino project for you to import to the IDE

For the Elite version, just create a simple or even empty script to download the project, since when in ‘normal’ operation you will just flash the Malduino once and then use the Micro-SD card to store new scripts.

A note on flashing, if you are using a Debian-based distribution you might come across some problems like I did and not be able to flash the device. Like the user on this most useful post, my modem-manager was trying to talk with the Malduino after every reset and confused AVRDUDE to death. The solution is to add udev rules to “/etc/udev/rules.d/77-mm-usb-device-blacklist-local.rules”, kudos to [socrim]:

ACTION!="add|change", GOTO="mm_usb_device_blacklist_local_end"
SUBSYSTEM!="usb", GOTO="mm_usb_device_blacklist_local_end"
ENV{DEVTYPE}!="usb_device", GOTO="mm_usb_device_blacklist_local_end"

ATTRS{idVendor}=="1b4f" ATTRS{idProduct}=="9204", ENV{ID_MM_DEVICE_IGNORE}="1"
ATTRS{idVendor}=="1b4f" ATTRS{idProduct}=="9203", ENV{ID_MM_DEVICE_IGNORE}="1"

LABEL="mm_usb_device_blacklist_local_end"

The Software

Since I’m running Linux, a quick shortcut to run a command is the ALT-F2 combination. So I script that into a file and save it to 1111.txt. The Elite searches the Micro-SD card for a file corresponding to the current dip switch state. Lets say the dip switch 2 and 4 are ON. In this case, the software tries to find the file named 0101.txt and parse its contents (as in dip switch order 1,2,3,4 and not the binary representation of the number 2 and 4) . When it finishes, the red LED starts flashing quickly. My simple script was:

DELAY 2000
ALT F2
DELAY 1000
STRING xterm
DELAY 1000
ENTER
DELAY 1000
STRING id
DELAY 1000
ENTER

But it was not working. Almost all commands worked but the ALT-F2 combo was not functioning properly. Close, but no cigar. No ALT-F2, no run command window. I’ve already lazy-browsed the source code a bit because I really didn’t have a lot of time on my hands but I needed to figure this out. The offending code was this:

else if(equals(s,e,"F1",<strong>3</strong>)) Keyboard.press(KEY_F1);</pre>

else if(equals(s,e,"F2",<strong>3</strong>)) Keyboard.press(KEY_F2);
...
else if(equals(s,e,"F10",3)) Keyboard.press(KEY_F10);
else if(equals(s,e,"F11",3)) Keyboard.press(KEY_F11);

A custom equals function was receiving size 3 for the strings of the Function keys, like “F2”. It was ok for “F10”, “F11” and “F12”, but failed for the rest of the keys. Changing 3 to 2 did the trick, but my Portuguese keyboard layout started to interfere with other test scripts. So I changed the code to include PT and UK layouts, changing them in a #define at compile time.

It would be cool if it was possible to access the SD card from the computer as a regular USB volume. I don’t know exactly how feasible that is, but it does not come with the current firmware. I still wanted to be able to output the content of an arbitrary file on the SD card to the screen, so I added another script function called ECHOFILEHEX that outputs the content of a file in the SD card as escape characters. For example, if the file a.txt contains “AAA”, the script command ECHOFILEHEX a.txt would output “\x41\x41\x41”. This can be useful to echo binary files into printf or echo -e, in Linux hosts at least.

Meanwhile, I had some trouble reading the original code. You know, we all have different programming styles. Don’t get me wrong, I’ve been known to write some messed-up spaghetti code. I sometimes browse old projects looking for some libs or classes I coded and wonder ‘who the heck wrote this steaming pile of code?’ Me, it was me. Anyway, I started to change a bit here and there and ended up changing pretty much the entire code. That’s the beauty and the curse of open-source. If you’re curious you can check it out here.

Conclusion

All in all, and despite some bumps, I’m quite pleased with Malduino. It is what I expected: an open platform for BadUSB attacks that’s in its infancy. It’s awesome that we can all tinker with it, modify it, make it better or just make it suit our needs. I hope a real community can start so we can see its full potential emerge. My short list includes simulating other USB devices, better SD card management, and expanding the device via the unused pins. What would you add?

It’s a long way to go and a lot can go wrong, so good luck with the project [Seytonic]!

MalDuino is an Arduino-powered USB device which emulates a keyboard and has keystroke injection capabilities. It’s still in crowdfunding stage, but has already been fully backed, so we anticipate full production soon. In essence, it implements BadUSB attacks much like the widely known, having appeared on Mr. Robot, USB Rubber Ducky.

It’s like an advanced version of HID tricks to drop malicious files which we previously reported. Once plugged in, MalDuino acts as a keyboard, executing previous configured key sequences at very fast speeds. This is mostly used by IT security professionals to hack into local computers, just by plugging in the unsuspicious USB ‘Pen’.

[Seytonic], the maker of MalDuino, says its objective is it to be a cheaper, fully open source alternative with the big advantage that it can be programmed straight from the Arduino IDE. It’s based on ATmega32u4 like the Arduino Leonardo and will come in two flavors, Lite and Elite. The Lite is quite small and it will fit into almost any generic USB case. There is a single switch used to enable/disable the device for programming.

The Elite version is where it gets exciting. In addition to the MicroSD slot that will be used to store scripts, there is an onboard set of dip switches that can be used to select the script to run. Since the whole platform is open sourced and based on Arduino, the MicroSD slot and dip switches are entirely modular, nothing is hardcoded, you can use them for whatever you want. The most skilled wielders of BadUSB attacks have shown feats like setting up a fake wired network connection that allows all web traffic to be siphoned off to an outside server. This should be possible with the microcontroller used here although not native to the MalDuino’s default firmware.

For most users, typical feature hacks might include repurposing the dip switches to modify the settings for a particular script. Instead of storing just scripts on the MicroSD card you could store word lists on it for use in password cracking. It will be interesting to see what people will come up with and the scripts they create since there is a lot of space to tinker and enhanced it. That’s the greatness of open source.

You can watch the prototype in action in the video: