> For the complete documentation index, see [llms.txt](https://www.webassembly.guide/webassembly-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.webassembly.guide/webassembly-guide/webassembly/security.md). # Security WebAssembly is designed to be completely sandboxed. This is of critical importance for assuring maximum security of webpages. We would never like to visit a website and allow them to steal information from us. The same way that websites are sandboxed and safe, so should be WebAssembly. ### Why? These are the main reasons WebAssembly is secure: * **Memory safety**: WebAssembly programs have a linear memory that can't be accessed outside of its bounds. * **Undefined behavior**: is impossible thanks to the semantics of WebAssembly * **Code injection**: is literally impossible. All the functions used will needed to be declared at load time, and no functions can be generated at runtime (this also makes impossible having JITs in pure Wasm) * **Host functions**: By default WebAssembly have no access to the host Of all this properties, the host functions could be the most sensitive, but also the ones that can give us more control over the things that our WebAssembly program is able to execute. **Which of these statements is true?** * WebAssembly is as secure as Internet Explorer with ActiveX * WebAssembly is designed to be safe and sandboxed * We can have JITs compiled into WebAssembly * A Host function can't be insecure --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://www.webassembly.guide/webassembly-guide/webassembly/security.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.