WebAssembly 3.0

Apply these rules to WebAssembly Core 3.0 modules and the host code that loads and executes them. Apply browser, WASI, and shared-memory rules only when those facilities are used; WASI, the Component Model, and threads are separate specifications, not guarantees supplied by Core 3.0.

Version scope and provenance

• Verify the module's required features against every deployed engine version, compilation backend, and enabled feature configuration; Core 3.0 does not prescribe a single browser or runtime release.
• Set an explicit feature policy for validation and execution. Account for Core 3.0 memory64/table64, multiple memories, GC, typed function references, tail calls, exception handling, and relaxed SIMD; admit additional proposals only after reviewing their boundaries. Turn off features the workload doesn't use, including ones the engine enables by default: in Wasmtime, switch off GC and exceptions with Config::wasm_gc(false) and Config::wasm_exceptions(false) when guests don't use them, and Component Model async with Config::wasm_component_model_async(false) when components don't.
• On Wasmtime 39.0.0 through 48.0.3 and 49.0.0 through 49.0.1, which predate the fix in 48.0.4 and 49.0.2, a hostile component can use Component Model async callbacks to write to the host's native stack. On those releases, before loading untrusted components, either turn Component Model async off, with Config::wasm_component_model_async(false), -W component-model-async=n in the CLI, or a build without the component-model-async Cargo feature, or reject invalid components first