We present a new scalable, semi-supervised method for inferring taint analysis specifications by learning from a large dataset of programs. Taint specifications capture the role of library APIs (source, sink, sanitizer) and are a critical ingredient of any taint analyzer that aims to detect security violations based on information flow.
The core idea of our method is to formulate the taint specification learning problem as a linear optimization task over a large set of information flow constraints. The resulting constraint system can then be efficiently solved with state-of-the-art solvers. Thanks to its scalability, our method can infer many new and interesting taint specifications by simultaneously learning from a large dataset of programs (e.g., as found on GitHub), while requiring few manual annotations.
We implemented our method in an end-to-end system, called Seldon, targeting Python, a language where static specification inference is particularly hard due to lack of typing information. We show that Seldon is practically effective: it learned almost 7,000 API roles from over 210,000 candidate APIs with very little supervision (less than 300 annotations) and with high estimated precision (67%). Further,using the learned specifications, our taint analyzer flagged more than 20,000 violations in open source projects, 97% of which were undetectable without the inferred specifications.