  Dataflow diagrams (DFDs) are a valuable asset for securing applications, as
they are the starting point for many security assessment techniques. Their
creation, however, is often done manually, which is time-consuming and
introduces problems concerning their correctness. Furthermore, as applications
are continuously extended and modified in CI/CD pipelines, the DFDs need to be
kept in sync, which is also challenging. In this paper, we present a novel,
tool-supported technique to automatically extract DFDs from the implementation
code of microservices. The technique parses source code and configuration files
in search for keywords that are used as evidence for the model extraction. Our
approach uses a novel technique that iteratively detects new keywords, thereby
snowballing through an application's codebase. Coupled with other detection
techniques, it produces a fully-fledged DFD enriched with security-relevant
annotations. The extracted DFDs further provide full traceability between model
items and code snippets. We evaluate our approach and the accompanying
prototype for applications written in Java on a manually curated dataset of 17
open-source applications. In our testing set of applications, we observe an
overall precision of 93% and recall of 85%.
