Deploying Wasm Securely

WebAssembly, or Wasm, offers revolutionary possibilities for web development, but like all technologies, it brings its own set of security challenges.

Foundations of Wasm Security

  • Wasm operates inside a sandbox. This means it’s isolated from the system it runs on, reducing potential risk
  • WebAssembly’s execution model is strict, ensuring behaviors are consistent, which is crucial for security.

Security Challenges with Wasm

  • As a low-level binary format, Wasm is difficult to read, making it a potential hiding place for malicious code
  • High-performance tasks in Wasm can clog CPU resources, leading to potential DoS attacks
  • Certain browser optimizations for Wasm might be susceptible to attacks like Spectre

Hands-on Tutorial

Environment Setup

Ensure your Wasm environment is up-to-date.

$ cargo install was time

Compile with Limited Permissions

Define your Wasm functions with minimal permissions. Avoid unnecessary imports or exports.

// Rust code targeting Wasm
#[no_mangle]
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

Validate and Sanitize Inputs

Protect against malicious or unexpected inputs.

// Loading Wasm in JavaScript
WebAssembly.instantiate(wasmModule).then(results => {
    let add = results.instance.exports.add;
    let input1 = sanitizeInput(userInput1);
    let input2 = sanitizeInput(userInput2);
    console.log(add(input1, input2));
});

function sanitizeInput(input) {
    // For this example, ensure input is a number and within a safe range
    let num = parseInt(input);
    return (isNaN(num) || num > 1000000) ? 0 : num;
}

Memory Safety with Wasm

WebAssembly provides a linear memory model. However, improper memory management can still be a risk. Use language features and tools that prevent buffer overflows and memory access violations.

For example, when working with Rust and Wasm, Rust’s ownership model helps prevent many memory safety issues. Still, always be cautious with raw pointers and unsafe blocks.

Safe Third-party Modules

Ensure that third-party modules are from reputable sources. Check for known vulnerabilities and always use the latest, patched versions.

# Using `wasm-pack` to build Rust code to Wasm, and then audit for vulnerabilities
$ wasm-pack build
$ cargo audit