Esbuild version 0.0.16 is a minor iteration building upon the foundation laid by its predecessor, version 0.0.15, in the realm of JavaScript bundling and minification. Both versions tout Esbuild's core promise: blazing-fast performance. Developers seeking to optimize their build processes for speed will find either version compelling. Both versions share identical descriptions: "An extremely fast JavaScript bundler and minifier," maintain the same MIT license, ensuring freedom in usage and modification, and are hosted within the same GitHub repository. The packaged code has the same size and amount of files.
The key differentiator lies in the release date. Version 0.0.16 arrived on April 9, 2020, a mere two days after version 0.0.15 (released April 7, 2020). This suggests that version 0.0.16 likely incorporates bug fixes, small enhancements, or refinements identified shortly after the release of 0.0.15. While the core functionality remains consistent, developers are generally encouraged to adopt the latest available version within a minor release series to benefit from these potential improvements. Upgrading from 0.0.15 to 0.0.16 presents a low-risk opportunity to ensure you're leveraging the most polished iteration of this ultra-fast bundler. For new projects choosing esbuild, starting directly with 0.0.16 can be a reasonable default strategy.
All the vulnerabilities related to the version 0.0.16 of the package
esbuild enables any website to send any requests to the development server and read the response
esbuild allows any websites to send any request to the development server and read the response due to default CORS settings.
esbuild sets Access-Control-Allow-Origin: * header to all requests, including the SSE connection, which allows any websites to send any request to the development server and read the response.
https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/pkg/api/serve_other.go#L121 https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/pkg/api/serve_other.go#L363
Attack scenario:
http://malicious.example.com).fetch('http://127.0.0.1:8000/main.js') request by JS in that malicious web page. This request is normally blocked by same-origin policy, but that's not the case for the reasons above.http://127.0.0.1:8000/main.js.In this scenario, I assumed that the attacker knows the URL of the bundle output file name. But the attacker can also get that information by
/index.html: normally you have a script tag here/assets: it's common to have a assets directory when you have JS files and CSS files in a different directory and the directory listing feature tells the attacker the list of files/esbuild SSE endpoint: the SSE endpoint sends the URL path of the changed files when the file is changed (new EventSource('/esbuild').addEventListener('change', e => console.log(e.type, e.data)))The scenario above fetches the compiled content, but if the victim has the source map option enabled, the attacker can also get the non-compiled content by fetching the source map file.
npm inpm run watchfetch('http://127.0.0.1:8000/app.js').then(r => r.text()).then(content => console.log(content)) in a different website's dev tools.Users using the serve feature may get the source code stolen by malicious websites.