JSON Parser


The firmware is extracted from an IoT device that needs parsing some files and in this use-case JSON files. Only the JSON parsing part of the firmware is available. The MCU running this firmware is a STM32F412.

The goal is exploring the implementation with TritonDSE to try finding vulnerabilities.

Practical information

  • The code is ARM Thumb-2

  • Base address is: 0x08000000

  • Entrypoint is: 0x81dc46e | 1

  • Exit point: (can be set to instruction just after)

The entrypoint is a call on the function parsing the JSON input. Its prototype is the following:

int json_parser(char* buffer, int len, JSON_ctx* ctx);

While the two first parameters are straightforward. The third is an object for which we don’t know the exact structure.


  • Load the firmware into a SymbolicExplorator (see the Loaders section of the tutorial).

  • Try out different exploration strategies and visualize the resulting coverage in Lighthouse.

    • Different CoverageStrategy values.

    • Inject one one parameter at the time then multiple ones (see How to inject arbitrary variables in the Seeds section of the tutorial).

  • Use Sanitizers to detect potential bugs.


The JSON_ctx structure contains two callback functions that you will need to stub (using hooks) to enable emulation to be carried to the end.

  • Make sure both buffers buffer and ctx points to a recognizable memory area.