Esbuild is a blazing-fast JavaScript bundler and minifier, and versions 0.3.2 and 0.3.3 showcase its rapid development pace. Both versions offer developers an efficient tool for optimizing web applications, prioritizing speed and performance. They share the same license, MIT, signifying a commitment to open-source principles and ease of use. The core functionality, indicated by identical fileCount and unpackedSize, remains consistent between the two releases promising stability while providing constant improvement.
The most notable difference lies in the release date: version 0.3.3 arrived just three days after 0.3.2 suggesting either rapid bug fixes or minor feature additions. For developers, this quick iteration highlights the project's responsiveness and dedication to delivering timely enhancements. While the specifics of what changed in these three days remain unspecified in the metadata, the proximity of releases encourages users to upgrade to 0.3.3 to potentially benefit from the latest refinements and optimizations improving developer experience and production performance. Reviewing the changelog on the project's GitHub repository (indicated by the repository URL) provides the most comprehensive understanding of enhancements. This fast paced change promises developer-oriented solution for bundling and minifying JavaScript and front-end assets.
All the vulnerabilities related to the version 0.3.3 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.