Finding Security Bugs

Reviewed by Greg Wilson / 2016-04-26
Keywords: Security

Near2016 Joseph P. Near and Daniel Jackson: "Finding security bugs in web applications using a catalog of access control patterns". Proceedings of the 38th International Conference on Software Engineering, 10.1145/2884781.2884836.

We propose a specification-free technique for finding missing security checks in web applications using a catalog of access control patterns in which each pattern models a common access control use case. Our implementation, SPACE, checks that every data exposure allowed by an application's code matches an allowed exposure from a security pattern in our catalog. The only user-provided input is a mapping from application types to the types of the catalog; the rest of the process is entirely automatic. In an evaluation on the 50 most watched Ruby on Rails applications on Github, SPACE reported 33 possible bugs—23 previously unknown security bugs, and 10 false positives.

A lot of programmers use object-relational mapping systems (ORMs) that provide a more-or-less declarative interface between their code and their database. Far fewer have ever used tools like Alloy, which allow them to model the ways their program is supposed to behave, then look for counter-examples that violate those constraints. In this paper, the authors use Alloy to look for security bugs in Rails applications; the user has to express what's allowed as a set of role-based access control (RBAC) constraints, and then the tool looks for execution paths in the code that don't obey those rules.

The three most impressive things in this work for me are (a) how straightforward the modeling is, (b) how low the false positive rate is, and (c) the fact that Alloy's home page includes a link to questions about it on Stack Overflow. One thing I didn't find was a link to the source: as far as I can tell, the underlying solver is available, but the only source I could find for Alloy itself bills itself as "an unofficial copy". If anyone can clarify its availability, please let us know.