new post: Digispark attiny85 bad USB

2026-08-30 21:26:41 +02:00
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+---
+layout: post
+author: Sam Hadow
+tags: cybersecurity hardware
+---
+
+This short blog post explains how to use a Digispark Attiny85 as a [bad USB](https://en.wikipedia.org/wiki/BadUSB) device.
+
+# Steps
+
+## 0. The board itself
+
+The board looks like this:
+
+![Picture 1]( /assets/img/2026-08-30-bad-usb-with-a-digispark-attiny85/1.png )
+![Picture 2]( /assets/img/2026-08-30-bad-usb-with-a-digispark-attiny85/2.png )
+
+And with a 3d printed case like [this one](https://www.printables.com/model/509019-digispark-attiny85-enclosure-bad-usb-stick-fake-me) it can even look like a somewhat genuine USB stick:
+
+![Picture 3]( /assets/img/2026-08-30-bad-usb-with-a-digispark-attiny85/3.png )
+
+## 1. Preparing the environment
+
+### 1.1. Installing Arduino IDE and the required libraries
+
+First install `micronucleus`, on Archlinux this can be done with the command `sudo pacman -S micronucleus`  
+Then install the [Arduino IDE](https://github.com/arduino/arduino-ide). On Archlinux it's available in the AUR as the package `arduino-ide-bin`.  
+
+### 1.2. Installing the boards manager
+
+Open Arduino IDE and go to File > Preferences and in the field "Additional Board Manager URLs:" add:
+```
+https://raw.githubusercontent.com/digistump/arduino-boards-index/master/package_digistump_index.json
+```
+If you have multiple additional board manager URLs you can separate them with `,`
+
+Then in Tools > Board > Boards Manager, search for "digispark" and install "Digistump AVR Boards"
+
+## 2. Flashing a payload
+
+Select in Tools > Board > Digistump AVR Boards, the board "Digispark (Default - 16.5mhz)"  
+Then create a sketch and write your bad USB payload, for example:
+
+```c++
+#include "DigiKeyboard.h"
+
+void setup() {
+  // Give Linux time to enumerate the Digispark as a keyboard.
+  DigiKeyboard.delay(1000);
+
+  // Open a terminal.
+  DigiKeyboard.sendKeyStroke(KEY_T, MOD_CONTROL_LEFT | MOD_ALT_LEFT);
+  DigiKeyboard.delay(1000);
+
+  // Launch Firefox.
+  DigiKeyboard.print("firefox https://hadow.fr");
+  DigiKeyboard.sendKeyStroke(KEY_ENTER);
+}
+
+void loop() {
+}
+```
+
+(Please note that this payload will work only with a QWERTY layout)
+
+You can also find payloads [here](https://github.com/CedArctic/DigiSpark-Scripts) and [here](https://github.com/MTK911/Attiny85)
+
+Then upload the sketch, in the output you should see:
+```
+Sketch uses 2944 bytes (48%) of program storage space. Maximum is 6012 bytes.
+Global variables use 162 bytes of dynamic memory.
+Running Digispark Uploader...
+Plug in device now... (will timeout in 60 seconds)
+> Please plug in the device ... 
+> Press CTRL+C to terminate the program.
+```
+Plug in your device and you should see:
+```
+> Device is found!
+connecting: 16% complete
+connecting: 22% complete
+connecting: 28% complete
+connecting: 33% complete
+> Device has firmware version 1.6
+> Available space for user applications: 6012 bytes
+> Suggested sleep time between sending pages: 8ms
+> Whole page count: 94  page size: 64
+> Erase function sleep duration: 752ms
+parsing: 50% complete
+> Erasing the memory ...
+erasing: 55% complete
+erasing: 60% complete
+erasing: 65% complete
+> Starting to upload ...
+writing: 70% complete
+writing: 75% complete
+writing: 80% complete
+> Starting the user app ...
+running: 100% complete
+>> Micronucleus done. Thank you!
+```
+
+You can then unplug your device and plug it into a computer to execute the payload.  
+**Disclaimer:** Only plug in this device in computers you are allowed to.
+
+This short blog post also demonstrates why you should never pick up random USB sticks from the ground and plug them into your computer.
+
+