Esbuild is a blazing-fast JavaScript bundler and minifier, and versions 0.12.17 and 0.12.18 offer compelling solutions for developers seeking optimal build performance. Both versions are MIT licensed, ensuring open-source flexibility, and share core characteristics, including the same unpacked size and file count within the distributed package. Crucially, both packages boast the same core functionally.
The primary difference lies in their release dates. Version 0.12.18 landed on August 5th, 2021, a week after version 0.12.17 released on July 29th, 2021. While the identical unpacked sizes suggest no significant changes to the core library size, the new version includes bug fixes and very small improvements. For developers, upgrading to 0.12.18 is advisable for maintaining the most stable and up-to-date version.
Esbuild's speed and efficiency make it a valuable tool for modern web development workflows. Developers gain benefits like faster build times, crucial for large projects and continuous integration environments. Its ability to bundle and minify JavaScript significantly optimizes web application performance, leading to improved user experience and SEO scores. The library is also suitable for use cases where rapid prototyping or quick iterations are important. Esbuild continues to be a great option for web performance and an important part of a developer's toolbelt.
All the vulnerabilities related to the version 0.12.18 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.