Esbuild version 0.9.6 builds upon the already impressive foundation of its predecessor, version 0.9.5, continuing to deliver an extremely fast JavaScript bundling and minification experience. Both versions maintain the core features that developers appreciate: speed, efficiency, and a permissive MIT license, making them suitable for a wide range of projects. Both versions also keep the same number of files inside the package (6). If you are using CI/CD pipelines it should not have affect on the pipeline speed.
However, the key difference lies in the unpacked size of the package, which has experienced a slight increase from 70447 bytes in version 0.9.5 to 75405 bytes in version 0.9.6. This 7% increase suggests that version 0.9.6 likely includes additional features, optimizations, or bug fixes that contribute to a larger footprint. Developers should be aware of this size difference, especially those working in environments with strict size constraints.
Furthermore, version 0.9.6 was released on March 20, 2021, a day after version 0.9.5. This short interval between releases implies that version 0.9.6 might address immediate issues or improvements identified shortly after the release of version 0.9.5. Developers contemplating an upgrade should consider this accelerated release cycle and consult the official changelog or release notes for detailed information on the specific changes included in version 0.9.6. The library continues being an interesting option for developers that want to speed up their builds with a modern tool.
All the vulnerabilities related to the version 0.9.6 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.