Esbuild, a blazing-fast JavaScript and CSS bundler, released version 0.21.4 as a minor update following version 0.21.3. Both versions maintain the core functionality of providing incredibly quick bundling and minification, crucial for modern web development workflows. Examining the metadata reveals that the primary difference lies in the versioning of the optional dependencies. Each @esbuild/* platform-specific package sees its version bumped to 0.21.4, aligning with the core esbuild package. These optional dependencies cater to different operating systems and architectures, ensuring esbuild's compatibility across a diverse range of environments, from Windows (win32-x64, win32-ia32, win32-arm64) to Linux (x64, arm, arm64, s390x) and macOS (darwin-x64, darwin-arm64), even covering less common systems like FreeBSD, NetBSD, and Android.
Beyond the version increments in optional dependencies, a noteworthy change is the slight increase in unpacked size, going from 132,781 bytes in version 0.21.3 to 133,372 bytes in version 0.21.4. This suggests the introduction of some minor code adjustments, bug fixes, or optimizations. Developers might want to upgrade for potential stability improvements and subtle performance enhancements related to the core bundling algorithms or platform-specific functionalities. The release date difference highlights an active development cycle. For developers, this rapid iteration signals continuous improvement and responsiveness to community needs, making esbuild a reliable and evolving choice for their bundling requirements. While the core features remain consistent, staying up-to-date with the latest version ensures access to the most refined and optimized bundling experience.
All the vulnerabilities related to the version 0.21.4 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.