Esbuild, a blazing-fast JavaScript and CSS bundler and minifier, has released version 0.21.1, a minor update following closely after version 0.21.0. Both versions maintain consistent descriptions emphasizing their speed and core functionality as bundlers and minifiers. The key variation lies in the version numbers of included optional dependencies, which are platform-specific binaries designed to optimize performance across diverse operating systems and architectures. These optional dependencies, such as @esbuild/linux-x64 or @esbuild/darwin-arm64, all reflect the specific esbuild version they are bundled with (either 0.21.0 or 0.21.1 respectively).
For developers, this implies that upgrading from 0.21.0 to 0.21.1 primarily ensures the use of the very latest platform-optimized binaries. While the core esbuild functionality likely remains largely unchanged, these updated binaries may contain bug fixes or performance improvements tailored to specific environments. The fileCount and unpackedSize in the "dist" section are identical, suggesting no significant changes in the core library's size or structure between the two versions. However, the releaseDate confirms 0.21.1 came out shortly after 0.21.0, possibly to address any quickly-found issues or refinements suitable for immediate release. Upgrading is recommended for developers seeking the most current and potentially stable experience, even if the changelog remains unclear. The core functionalities of esbuild as a zero-config bundler are unnafected.
All the vulnerabilities related to the version 0.21.1 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.