Esbuild version 0.6.6 represents a minor update to the blazing-fast JavaScript bundler and minifier, succeeding version 0.6.5. While both versions maintain the same core description as an "extremely fast" tool for modern JavaScript development, subtle changes likely enhance performance or address specific bugs. Developers considering esbuild for optimizing their build processes will find that both versions share the MIT license, granting them broad usage rights. The source code for both versions remains accessible through the official GitHub repository (evanw/esbuild).
The key differences lie in the distribution details. Version 0.6.6 comes packaged as a tarball available at https://registry.npmjs.org/esbuild/-/esbuild-0.6.6.tgz and contains six files, with an unpacked size of 25505 bytes. Version 0.6.5, available at a similar URL but with the corresponding version number, also contains six files but has a slightly smaller unpacked size of 24327 bytes. This difference in size could indicate additions like updated dependencies, new features, or expanded documentation. Released on July 25, 2020, version 0.6.6 follows version 0.6.5, which was released five days prior on July 20, 2020, suggesting a rapid iteration pace. Developers should consult the official changelog or commit history on GitHub to understand the specific changes and improvements implemented in version 0.6.6, ensuring they leverage the latest optimizations for their projects.
All the vulnerabilities related to the version 0.6.6 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.