Esbuild, a blazing-fast JavaScript and CSS bundler, has released version 0.21.0, succeeding the previous stable version 0.20.2. Both versions maintain the core promise of speed and efficiency in bundling and minifying web assets, crucial for modern web development workflows. A key distinction lies in the versioning of the optional dependencies. Both versions include a comprehensive set of optional dependencies tailored to various operating systems and architectures, such as @esbuild/linux-x64, @esbuild/darwin-arm64, and @esbuild/win32-arm64, ensuring compatibility across diverse platforms. However, version 0.21.0 updates these dependencies to version 0.21.0, while 0.20.2 uses version 0.20.2.
While the core functionality advertised by the "description" field remains the same, the upgrade to 0.21.0 likely includes bug fixes, performance improvements, and potentially new features or enhancements within the esbuild core and these platform-specific binaries. Developers should consider upgrading to 0.21.0 to benefit from these improvements and ensure they are using the most up-to-date and stable version of the tool. The small difference in unpackedSize between the two version may reflect some subtle changes in the binaries delivered by those packages. The releaseDate indicates a considerable gap between the two versions, which may also point at the accumulation of several bug fixes and enhancements. While the upgrade seems safe, thorough testing is always recommended, after upgrading any library in a production environment.
All the vulnerabilities related to the version 0.21.0 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.