Wednesday, 22 April 2026

WebAssembly Not Automatically Blocked by Browsers

WebAssembly is a type of code designed to run in modern web browsers.  It is designed to run alongside JavaScript using WebAssembly JavaScript APIs - creating an option for performance critical functionality.

As WebAssembly increases the browser's attack surface, so browsers contain WASM inside the browser's sandbox and restricts system access. 

A risk maybe breaking out of the sandbox. Adobe Flash was a product sandboxed after a bunch of exploits, and after sandboxing exploits still occurred.

Transmission of WASM does not require TLS, HSTS or any other transport layer security mechanism making it susceptible to man-in-the-middle attacks.

Integrity checking is also impossible as WASM modules need not be signed by the author.

Some security-focused browser configurations can block WASM.

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