Welcome to Chucky’s documentation!

This document is for this modified version of Chucky implementation and is also suitable for the original version (developed by Alwin Maier and Fabian Yamaguchi).

Introduction of Chucky

Chucky is a missing check vulnerability detection method designed by Fabian Yamaguchi. It statically taints source code and identifies anomalous or missing conditions linked to security-critical objects. Chucky analyzes functions for anomalies. To this end, the usage of symbols used by a function is analyzed by comparing the checks used in conjunction with the symbol with those used in similar functions.

The Implementation

This implemetation of Chucky interactive with the database parsed by joern (another tools developed by Fabian et al). After a Robust Parsing by joern, conditions, assignments and API symbols are extracted from every function and all the code information are stored in the graph database as Code Property Graphs including AST,CFG and DDG. Joern use Neo4j to store these information.

There are five step for Chucky to complete the analyze.

  1. Identification of sources and sinks. The query symbol is given by user as an analyse target. So the first job of Chucky is to locate them in the database and find all the candidates(functions that use the query symbol). According to different symbol types, this can be achived by a group of a well defined gremlin query.

  2. Neighborhood discovery.

    • Viewing the function as a document and defining the key words as the element concerned in the AST, Chucky describe each function as a symbol vector.
    • Chucky find the similarest top k functions to the query function by applying the information retrieval technique in this vector space.

    The first procedure is implemented by gremlin query in joern-tools and the second one is implemented by pure python.

  3. Lightweight tainting.

    Idendify the the condition code of if, while and for in which there exists a symbol in the path from the source to the sink. These symbols may influence or be influenced by the the query symbol in each top k similarest functions. This step is also implemented by gremlin queries as such relations can be described as a path in the code property graph.

  4. Embedding of functions.

    Describe each function as a sparse 0-1 vector according to the existence of the condition key words discovered by the pervious step.

  5. Anomaly detection.

    Find the most significant missing word in the condition vector of the query function set off by the neighborhoods. The anomaly score of the query function is expressed by the percentage of time the significant missing key word exists in the neighborhoods.

All the analysis are based on the extensible query language defined in joern-tools by Gremlin and a wrapped inteface defined by python-joern.

For the orginal idea, please refer to Chucky: Exposing Missing Checks in Source Code for Vulnerability Discovery Fabian Yamaguchi, Christian Wressnegger, Hugo Gascon, and K. Rieck ACM Conference on Computer and Communications Security (CCS)

About the Modification.

  1. Refactor to clean the middle code.
    • Replace sally embedding module by pure python code(transplant the code witten by Fabian) to remove the data exchange cost on disk.
    • Fix some bugs and make it more robust.
  2. Rewirte the KNN class to support the neighborhood selection strategy:
    • Leverage the name(file name or function name) information and the caller set information of a function when it’s usefull.
    • Kick some name irrelevant functions out, and set a robust threshold for the recomandation of good candidate.
  3. Add multi-source/sink support.
    • Design a new option set for user to specify the multi-source/sink.
    • Use the combination of source/sink as the key feature to find candidate neighborhood.
    • Use the union of the tainted condition features as the condition embedding feature.
    • Refactor the job generation and remove the redundant function selection to improve the performance.
  4. Add a report module to show the detail report.

Note: the advancement of the modification still needs to be judged and more evaluation is required. Connect Ke Yang(123yangke321@sina.com) for more information.

Although this is a NON-OFFICIAL document for Chucky, hope it will be helpful for people who are intersted in Chucky and working and studying in this area.