Esbuild, a renowned JavaScript and CSS bundler and minifier known for its exceptional speed, recently released version 0.21.2, succeeding the previous stable version 0.21.1. While both versions share the same core functionalities, description, license (MIT), and repository details, a closer inspection reveals subtle yet important distinctions. Both are designed to drastically reduce bundling times compared to other tools. the main package esbuild is just a wrapper around native builds of the bundler.
The primary difference lies in the version numbers within the optional dependencies. These dependencies, structured as @esbuild/{platform}, cater to specific operating systems and architectures (e.g., @esbuild/linux-x64, @esbuild/win32-arm64). In version 0.21.2, all optional dependencies are updated to "0.21.2", mirroring the main package version. Similarly, version 0.21.1 has all of its optional dependencies versioned at "0.21.1".
Release dates also differ. Version 0.21.2 was released on May 12, 2024, while version 0.21.1 was released on May 7, 2024. This indicates that version 0.21.2 is the newer release, likely containing bug fixes, performance improvements, or support for newer platforms addressed since the prior release.
Developers leveraging esbuild should prioritize using the latest version (0.21.2) to benefit from the most recent enhancements and ensure compatibility with their target environments. The consistently updated optional dependencies signal ongoing maintenance and expansion of platform support, making esbuild a reliable choice for projects targeting diverse deployment environments. Specifically, check the optional dependencies names to see all supported environments.
All the vulnerabilities related to the version 0.21.2 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.