>This is all overwhelmingly worse than in the native case, because we make some effort to run only trustworthy native code, but browsers actively solicit unknown code from known-hostile sources--most particularly, web ads. The existence of safe-ish languages doesn't help, because there is no incentive to deploy them in user-hostile code fragments.

WebAssembly strongly sandboxes WASM modules that are executed, so the situation where an attacker creates and serves a malicious WASM module to the user's browser is one that is handled well.

The article is saying that WASM's protections stop a module from escaping its sandbox, but it doesn't prevent a buggy module from having its own memory get corrupted by its own memory-related bugs common in unsafe languages.