Esbuild version 0.8.5 is a minor update to the blazing-fast JavaScript bundler and minifier, building upon the solid foundation established in version 0.8.4. While both versions share the same core functionality – offering incredibly quick build times suitable for projects of all sizes and complexities – subtle improvements have been introduced in this latest iteration. Developers migrating from 0.8.4 to 0.8.5 can anticipate a refinement of the already impressive performance, potentially experiencing faster build speeds or more efficient memory usage.
The size difference between the two releases is minimal, with version 0.8.5 having a slightly larger unpacked size 51054 compared to 0.8.4's 50746. This small increase suggests the incorporation of new features, refinements, or bug fixes. Although the changelog for this specific minor version isn't detailed, the very nature of esbuild's development emphasizes continuous improvement in areas like bundling algorithms, minification techniques, and overall stability.
For developers heavily reliant on esbuild for their build processes, adopting version 0.8.5 is recommended to leverage the latest enhancements. The release date difference from 2020-11-05 to 2020-11-07 indicates the developers actively maintain and refine the package. The promise of "extremely fast JavaScript bundling" remains central to both versions, making esbuild a strong contender for optimizing front-end development workflows.
All the vulnerabilities related to the version 0.8.5 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.