Fuddly – Fuzzing and Data Manipulation Framework

Among the variety of complementary approaches used in the security evaluation of a target (e.g., software, an embedded equipment, etc.), fuzz testing—abbreviated fuzzing—is widely recognized as an effective means to help discovering security weaknesses in a target.

Fuzzing is a software testing approach, which consists in finding design or implementation flaws by stepping outside the expectations the target may have relative to its input data, while looking out for any unexpected behavior. This approach strives to confuse the target in a way to specifically avoid rejection by possible conformity tests—performed by the target—while still having a chance to trigger more subtle bugs. For such purpose, various ways are worth considering like using malformed data, playing around the protocol sequencing, and so on. Fuzzing is similar to what is termed fault injection in the field of dependability.

fuddly is a fuzzing and data manipulation framework whose main objectives are:

  • To allow users to build data model that:
    • mix very accurate representations for certain aspects with much coarser ones for others that are outside the focus of the testing; leaving open the way of refining the other parts should the need arise;
    • may be combined with each other;
    • enable to dissect raw data for analyzing them and enable to absorb them within the data model for manipulation;
    • enable to mix up generation and mutation fuzzing techniques.
  • To represent the data in a way that simplify the process of fuzzing and especially to enable the implementation of elaborated transformations. By ‘’elaborated’’ we mean the capability to act on any data part (that is not necessarily contiguous) while preserving consistency of dependent parts if so desired. This amounts to allowing transformations to be articulated around syntactic criteria—e.g., modification of an integer depending on the size of the field hosting it—or semantic ones—e.g., alteration of a value regarding its meaning for a given data format or protocol, alteration of specific data sub-parts forming a sound group for a given data format or protocol.
  • To automate the fuzzing process relying on various fuddly’s sub-systems enabling: the communication with the target, to follow and monitor its behavior and to act accordingly (e.g., deviate from the protocol requirements like sequencing, timing constraints, and so on), thanks to data model search and modification primitives, while recording every piece of information generated during this process and enabling to replay it.



  • Compatible with Python2 and Python3
  • Mandatory:
    • six: Python 2/3 compatibility
    • sqlite3: SQLite3 data base
  • Optional:
    • xtermcolor: Terminal color support
    • graphviz: For graphic visualization (e.g., scenario display)
    • paramiko: Python implementation of the SSHv2 protocol
    • serial: For serial port access
    • cups: Python bindings for libcups
    • rpyc: Remote Python Call (RPyC), a transparent and symmetric RPC library
  • For testing:
    • ddt: Used for data-driven tests
    • mock: Used for mocking (only needed in Python2)
  • For documentation generation:
    • sphinx: sphinx >= 1.3 (with builtin napoleon extension)
    • texlive (optional): Needed to generate PDF documentation
    • readthedocs theme (optional): Privileged html theme for sphinx


Fuzzing and Data Manipulation Framework: fuddly documentation

Fuzzing and Data Manipulation Framework: fuddly Download

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