Esbuild is a blazing-fast JavaScript bundler and minifier, and versions 0.4.7 and 0.4.8 showcase its rapid development pace. While seemingly incremental, the jump from 0.4.7 to 0.4.8, both released on the same day (June 5th, 2020), reveals subtle improvements valuable to developers. The crucial difference lies in the "unpackedSize" and "releaseDate", with version 0.4.8 slightly larger (20805 bytes vs 20349 bytes) and released later in the day. This suggests that version 0.4.8 included bug fixes, performance tweaks, or minor feature additions discovered or implemented after the initial 0.4.7 release. For developers using esbuild, even such minor version bumps are worth noting. While the core functionality likely remained the same, opting for 0.4.8 ensures a more refined and potentially more stable experience. Given esbuild's core proposition of speed, these incremental optimizations can translate to faster build times, even in already optimized workflows. For developers concerned with the latest refinements and bug fixes, choosing the newest available point release (0.4.8 in this case) is generally a best practice to leverage the continuous improvements made by the esbuild team, ensuring optimal performance.
All the vulnerabilities related to the version 0.4.8 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.