Rust is a multi-paradigm language with a focus on memory safety.

It aims to be system programming oriented, allowing fine-grained memory management without garbage collection but also without tedious and error-prone manual memory allocations and deallocations. It achieves this goal by means of its ownership system (mostly related to variable aliasing). At any point of a Rust program, the compiler tracks how many variables refer to a given data, and enforces a set of rules which enable automatic memory management, memory safety and data-race free programs.

The language also focuses on performance, with powerful compilation optimizations and language constructs that allow writing zero-cost abstraction code.

Moreover, the Rust language provides some high-level programming features. Thanks to higher-order functions, closures, iterators, etc., it allows to write program parts in the same vein as in functional programming languages. Besides, static typing discipline, type inference, and ad hoc polymorphism (in the form of traits) are other ways Rust provides to build libraries and programs in a safe manner.

Nevertheless, due to its versatility, the language possibly offers some constructions that, if not used properly, can introduce security problems, by making code misinterpreted by the programmer or a reviewer. In addition, as for every tool in the compilation or software verification field, the tools used to develop, compile and execute programs can expose certain features or configurations that, if misused, may lead to vulnerabilities.

Thus, the object of this document is to compile hints and recommendations to stay in a safe zone for secure applications development while taking advantage of the range of possibilities the Rust language can offer.

The guide intents to group recommendations that should be applied for application development with strong security level requirements. Anyway, it can be followed by everyone who wants to ensure that guarantees offered by the Rust platform are not invalidated due to unsafe, misleading or unclear feature usage.

It is not intended to be a course on how to write Rust programs, there are already plenty of good learning resources for this purpose (see for instance the Rust documentation main page). The purpose is rather to guide the programmer and inform him about some pitfalls he may encounter. These recommendations form a complement to the good level of trust the Rust language already provides. That said, recalls are sometimes necessary for clarity, and the experienced Rust programmer may rely solely on highlighted inserts (Rule, Recommendation, Warning, etc.).

This guide is written in a collaborative and open manner, via the GitHub platform (https://github.com/ANSSI-FR/rust-guide). All contributions for future versions are welcome, whether in the form of direct propositions (pull requests) or in the form of suggestions and discussions (issues).

This document considers separately different phases of a typical (and simplified) development process. Firstly, we provide some advices on how to take advantage of using tools of the Rust ecosystem for secure development. A following chapter focuses on precautions to take when choosing and using external libraries. Then, recommendations about the Rust language constructs are exposed.

A summary of recommendations presented throughout the document is listed at the end of this guide.