Alias-Aware Propagation of Simple Pattern-Based Properties in PHP Applications

In this paper, we present novel algorithms for the propagation of pattern-based properties in PHP applications. Intuitively, pattern-based properties designate those properties that are intrinsically associated to syntactic patterns in the source code. Security checks in access control models are an example of pattern-based properties. At the source code level, permissions are typically verified with stereotyped constructs, called security checks, that can be detected with syntactic patterns. Depending on the program, pattern-based properties can be a liased to variables that are propagated through the application. In that context, support from data-flow approaches is needed to track the propagation of patterns through the application. In the context of this paper, we focus on the alias-aware propagation of security checks through PHP applications. Specifically, we investigated the propagation of security checks in 8 PHP applications that implement access control models. We show how, using the Data log language, one can implement conceptually complex data-flow algorithms in an incremental, intuitive and compact manner. From the results perspective, we show how our algorithm identifies security checks and security check a liased variables in a precise way. The reported false positive rate varies between 0% and 4% for the investigated applications.