dont-sniff-mimetype

What is dont-sniff-mimetype?

The dont-sniff-mimetype npm package is a middleware for Express.js that helps prevent browsers from trying to guess (sniff) the MIME type of a response. This is important for security reasons, as MIME type sniffing can lead to security vulnerabilities such as Cross-Site Scripting (XSS) attacks.

What are dont-sniff-mimetype's main functionalities?

Set X-Content-Type-Options header

This feature sets the `X-Content-Type-Options` header to `nosniff` for all responses. This tells browsers not to perform MIME type sniffing, which helps prevent certain types of attacks.

const express = require('express');
const dontSniffMimetype = require('dont-sniff-mimetype');

const app = express();

// Use the dont-sniff-mimetype middleware
app.use(dontSniffMimetype());

app.get('/', (req, res) => {
  res.send('Hello, world!');
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Other packages similar to dont-sniff-mimetype

helmet

Helmet is a collection of 15 smaller middleware functions that set various HTTP headers to help secure your Express.js app. One of these middleware functions is `helmet.noSniff()`, which sets the `X-Content-Type-Options` header to `nosniff`, similar to dont-sniff-mimetype. Helmet provides a more comprehensive security solution compared to dont-sniff-mimetype.

nocache

nocache is a simple Express.js middleware that sets various HTTP headers to disable client-side caching. While its primary purpose is different from dont-sniff-mimetype, it also sets the `X-Content-Type-Options` header to `nosniff` as part of its functionality. This makes it a good alternative if you need to disable caching and prevent MIME type sniffing.

README

"Don't infer the MIME type" middleware

Some browsers will try to "sniff" mimetypes. For example, if my server serves file.txt with a text/plain content-type, some browsers can still run that file with <script src="file.txt"></script>. Many browsers will allow file.js to be run even if the content-type isn't for JavaScript.

Browsers' same-origin policies generally prevent remote resources from being loaded dangerously, but vulnerabilities in web browsers can cause this to be abused. Some browsers, like Chrome, will further isolate memory if the X-Content-Type-Options header is seen.

There are some other vulnerabilities, too.

This middleware prevents Chrome, Opera 13+, IE 8+ and Firefox 50+ from doing this sniffing. The following example sets the X-Content-Type-Options header to its only option, nosniff:

const nosniff = require('dont-sniff-mimetype')
app.use(nosniff())

MSDN has a good description of how browsers behave when this header is sent.