Wasmtime's Rust embedder API had an unsound handling of shared WebAssembly linear memories, allowing shared memories to be represented as non-shared memories. This could lead to data races in the host Rust code when shared memories are accessed concurrently. The issue arose from two API flaws: the Memory::new constructor accepting shared memory types improperly, and core dumps exposing shared memories unsafely. Patched versions reject shared memories via Memory::new and exclude them from core dumps.