  WebAssembly is the fourth officially endorsed Web language. It is recognized
because of its efficiency and design, focused on security. Yet, its swiftly
expanding ecosystem lacks robust software diversification systems. We introduce
WASM-MUTATE, a diversification engine specifically designed for WebAssembly.
Our engine meets several essential criteria: 1) To quickly generate
functionally identical, yet behaviorally diverse, WebAssembly variants, 2) To
be universally applicable to any WebAssembly program, irrespective of the
source programming language, and 3) Generated variants should counter
side-channels. By leveraging an e-graph data structure, WASM-MUTATE is
implemented to meet both speed and efficacy. We evaluate WASM-MUTATE by
conducting experiments on 404 programs, which include real-world applications.
Our results highlight that WASM-MUTATE can produce tens of thousands of unique
and efficient WebAssembly variants within minutes. Significantly, WASM-MUTATE
can safeguard WebAssembly binaries against timing side-channel
attacks,especially those of the Spectre type.
