AIKIDO-2026-898017

TL;DR

Wasmtime accepts WebAssembly components whose component model async callback function has an invalid type signature because the bundled wasmparser validator checks only the parameter count and never checks the result type. A malicious guest can use this to make the runtime write up to roughly 16KB of guest chosen data onto the host's native stack during an async lifted export call, overwriting return addresses and redirecting control flow to arbitrary host code or crashing the process, which escapes the sandbox. The fix corrects the callback signature validation so malformed components are rejected before they run.