Esbuild version 0.16.0 represents an incremental update focusing on internal package structure while maintaining core functionality. A key difference compared to version 0.15.18 lies in how platform-specific binaries are packaged. The older version (0.15.18) included binaries with names like "esbuild-linux-64" and "esbuild-windows-32" directly as dependencies. The newer version (0.16.0) refactors this by introducing scoped packages, such as "@esbuild/linux-x64" and "@esbuild/win32-ia32", for each platform. Functionally, this change shouldn't impact most users; esbuild should still automatically select the correct binary for your operating system. For developers, this change means that if you were directly referencing or manipulating these platform binaries within your build process (which is unlikely for most use cases), you will need to adjust your import paths to reflect the new scoped package names. Otherwise, the upgrade should be seamless which is awesome for javascript and css bundlers.
The core bundling and minification capabilities, as described in the shared description remain consistent across both versions. Both versions are designed to be extremely fast for bundling JavaScript and CSS. The update also seems to have created a minor increase in the unpacked size, approximately 1KB increase in size.
All the vulnerabilities related to the version 0.16.0 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.