WebAssembly (Wasm) is rapidly gaining popularity as a distribution format for software components embedded in various security-critical domains. Unfortunately, despite its prudent design, WebAssembly's primary use case as a compilation target for memory-unsafe languages leaves some possibilities for memory corruption. Independently of that, Wasm is an inherently interesting target for information flow analysis due to its interfacing role. Both the information flows between a Wasm module and its embedding context, as well as the memory integrity within a module, can be described by the hyperproperty noninterference. So far, no sound, fully static noninterference analysis for Wasm has been presented, but sound reachability analyses were. This work presents a novel and general approach to lift reachability analyses to noninterference by tracking taints on values and using value-sensitive, relational reasoning to remove them when appropriate. We implement this approach in Wanilla, the first automatic, sound, and fully static noninterference analysis for WebAssembly, and demonstrate its performance and precision by verifying memory integrity and other noninterference properties with several synthetic and real-world benchmarks.

WebAssembly (Wasm) is an increasingly deployed low-level language providing near-native performance to security-critical domains such as web browsers, smart contracts, and edge computing. In all of these domains, establishing the absence of bugs and security vulnerabilities is of utmost importance, which motivates the development of sound and automated static analysis techniques. This is, however, a challenging task since the Wasm formal semantics is not directly amenable to efficient static analysis, Wasm code is typically embedded in statically unknown and possibly malicious contexts, and the low-level nature of the language makes it hard to precisely and yet soundly capture memory management and other core features. In this work, we present Wappler, the first sound and automated static analysis technique for WebAssembly. The core idea is to encode the semantics into Horn clauses so as to make it accessible to automated theorem provers, such as z3. The realization of this approach, however, requires to tackle several challenges. We address the fact that the Wasm semantics is not directly amenable to automation of security proofs by introducing annotations that enable a precise, practical, and yet sound encoding. Furthermore, we devise a formalism to specify embedder behavior and introduce a sound yet precise memory abstraction. We demonstrate the expressiveness of our logical formalism by encoding several general as well as Wasm-specific security properties. Finally, we implement our static analysis technique and conduct an experimental evaluation over the official Wasm test suite to demonstrate its performance.

Traffic analysis attacks remain a significant problem for online security. Communication between nodes can be observed by network level attackers as it inherently takes place in the open. Despite online services increasingly using encrypted traffic, the shape of the traffic is not hidden. To prevent traffic analysis, the shape of a system's traffic must be independent of secrets. We investigate adapting the data-oblivious approach the reactive setting and present OblivIO, a secure language for writing reactive programs driven by network events. Our approach pads with dummy messages to hide which program sends are genuinely executed. We use an information-flow type system to provably enforce timing-sensitive noninterference. The type system is extended with potentials to bound the overhead in traffic introduced by our approach. We address challenges that arise from joining data-oblivious and reactive programming and demonstrate the feasibility of our resulting language by developing an interpreter that implements security critical operations as constant-time algorithms.

Traffic analysis attacks pose a major risk for online security. Distinctive patterns in communication act as fingerprints, enabling adversaries to de-anonymise communicating parties or to infer sensitive information. Despite the attacks being known for decades, practical solution are scarce. Network layer countermeasures have relied on black box padding schemes that require significant overheads in latency and bandwidth to mitigate the attacks, without fundamentally preventing them, and the problem has received little attention in the language-based information flow literature. Language-based methods provide a strong foundation for fundamentally addressing security issues, but previous work has overwhelmingly assumed that interactive programs communicate over secure channels, where messages are undetectable by unprivileged adversaries. This assumption is too strong for online communication where packets can be trivially observed by eavesdropping. In this paper we introduce SELENE, a small language for principled, provably secure communication over channels where packets are publicly observable, and we demonstrate how our program level defence can reduce the latency and bandwidth overheads induced compared with program-agnostic defence mechanisms. We believe that our results constitute a step towards practical, secure online communication.