Esbuild, a blazingly fast JavaScript and CSS bundler and minifier, has released version 0.20.1. Comparing it to the previous stable version, 0.20.0, reveals subtle but important changes of interest to developers. Both versions share the same core functionality – bundling and minifying code with exceptional speed. They both maintain their MIT license and repository on GitHub, ensuring open-source accessibility and community contribution. Additionally, both provide a comprehensive set of optional dependencies tailored to various operating systems and architectures, ranging from Windows and macOS to Linux and Android, supporting diverse hardware like x64, ARM, and even specialized architectures like RISC-V and MIPS. This extensive support ensures that esbuild can be optimized for performance across a wide range of deployment environments.
The key difference lies in the release date, with version 0.20.1 being released on February 19, 2024, while version 0.20.0 arrived on January 27, 2024. While the file count and unpacked size in the "dist" object are the same for both releases, the updated release date suggests that 0.20.1 likely incorporates bug fixes, performance tweaks, or minor feature enhancements implemented since the previous version. Developers should upgrade to the latest version (0.20.1) to benefit from these improvements, ensuring a more stable and optimized bundling experience. Check the release notes for detailed specifics on what has changed.
All the vulnerabilities related to the version 0.20.1 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.