2021 IEEE Symposium on Security and Privacy Workshops Accessible Formal Methods for Verified Parser Development Letitia W. Li, Greg Eakman Elias J. M. Garcia, Sam Atman FAST Labs, BAE Systems Special Circumstances Burlington, Massachusetts, USA Brussels, Belgium
[email protected],
[email protected] fejmg,
[email protected] Abstract—Security flaws in Portable Document Format (PDF) in the field of another object may not have been yet parsed, readers may allow PDFs to conceal malware, exfiltrate in- and therefore we cannot check any of the attributes of the ref- formation, and execute malicious code. For a PDF reader to erenced object (such as its type, or even its existence). Instead, identify these flawed PDFs requires first parsing the document syntactically, and then analyzing the semantic properties or these semantic properties are checked after the first parsing of structure of the parse result. This paper presents a language- the document, whether within the parser or separately. theoretic and developer-accessible approach to PDF parsing and In the DARPA SafeDocs project, we address the insecurity validation using ACL2, a formal methods language and theorem of PDF readers/parsers with a Language-theoretic Security prover. We develop two related components, a PDF syntax parser approach by first defining a PDF grammar, and then de- and a semantic validator. The ACL2-based parser, verified using the theorem prover, supports verification of a high-performance veloping verified parsers to accept only well-formed input equivalent of itself or an existing PDF parser. The validator then according to that grammar [8]. In this paper, we propose an extends the existing parser by checking the semantic properties accessible formal methods approach in ACL2 for safe, secure, in the parse result.