WasmRef-Isabelle: A Verified Monadic Interpreter and Industrial Fuzzing Oracle for WebAssembly

We present WasmRef-Isabelle, a monadic interpreter for WebAssembly written in Isabelle/HOL and proven correct with respect to the WasmCert-Isabelle mechanisation of WebAssembly. WasmRef-Isabelle has been adopted deployed as fuzzing oracle continuous integration infrastructure Wasmtime, widely used implementation. Previous efforts fuzz Wasmtime against WebAssembly's official OCaml reference were abandoned by Wasmtime's developers after exhibited unacceptable performance characteristics, which its maintainers decided not fix order preserve interpreter's close definitional correspondence specification. With we achieve best both worlds - an fast enough be useable that also maintains specification through mechanised proof correctness. verify correctness two-step refinement Isabelle/HOL. demonstrate significantly outperforms interpreter, comparable Rust debug build industry Wasmi, competes unverified oracles on throughput when infrastructure. several new extensions enhance WasmRef-Isabelle's utility oracle: add support number upcoming features, fully mechanise numeric semantics integer operations.