Esbuild is a blazing-fast JavaScript bundler and minifier, and versions 0.8.55 and 0.8.54 offer developers a powerful tool for optimizing web performance. While seemingly similar with identical file counts (6) and unpacked sizes (71788), the key distinction lies in their release dates. Version 0.8.55 was published on March 4th, 2021, following version 0.8.54 which was released on March 1st, 2021. This indicates that version 0.8.55 incorporates any bug fixes, performance improvements, or minor feature updates implemented in the intervening three days.
For developers, this means choosing version 0.8.55 likely provides the most stable and refined experience. While the core functionality remains consistent, adopting the newer version ensures you benefit from the latest refinements provided by the esbuild team. As a library focused on speed and efficiency, even incremental improvements can contribute to faster build times and optimized code output. Always check the official changelog for granular details on specific changes, but typically these frequent updates aim for better stability and potentially improved compatibility with evolving JavaScript standards and frameworks. Therefore, upgrading to 0.8.55 is recommended for a more modern and polished bundling experience.
All the vulnerabilities related to the version 0.8.55 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.