Esbuild version 0.19.3 represents a minor but potentially impactful update over its predecessor, version 0.19.2. Both versions maintain the core functionality of being an extremely fast JavaScript and CSS bundler and minifier, a key selling point for developers seeking performance optimization in their build processes. The foundational dependencies and optional dependencies remain largely the same, ensuring consistent platform support across various operating systems and architectures, including Linux, Windows, macOS, Android, and FreeBSD. The versions are almost identical and the package names are the same, the biggest difference is the version number and the date when the version was released.
The primary distinctions lie in the release date and potentially subtle bug fixes or performance improvements. Version 0.19.3 was released on September 14th, 2023, approximately a month after version 0.19.2, which was released on August 14th, 2023. The unpacked size of the new version is slightly bigger and went from 131511 to 131520. While the core API and features remain consistent, developers are encouraged to upgrade to version 0.19.3 to leverage any improvements in stability, security, or bundling efficiency. Checking the changelog or release notes accompanying the new version is crucial for understanding the specific changes implemented. The MIT license ensures developers can freely use and modify the tool. Developers who prioritize staying current with the latest enhancements and fixes should consider adopting version 0.19.3.
All the vulnerabilities related to the version 0.19.3 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.