Esbuild 0.19.8 represents a minor version update to the blazing-fast JavaScript and CSS bundler and minifier, following closely on the heels of version 0.19.7. While the core description highlighting its speed and functionality remains consistent, a closer examination reveals subtle yet important differences. Both versions maintain an extensive list of dependencies and optional dependencies, with each dependency specifically tailored for various operating systems and architectures, like Linux (arm, x64, arm64, and more), Windows (x64, ia32, arm64), macOS (x64, arm64), Android, FreeBSD, and others. The key difference lies in the version numbers of these architecture-specific dependencies; in 0.19.8, they're updated to 0.19.8 accordingly, ensuring consistency and potentially incorporating bug fixes or performance improvements specific to those platforms. Similarly, the optional dependencies also mirror this version bump. The license remains MIT, and the repository URL stays the same, indicating no fundamental changes to the licensing or source code location. The distribution files are also very similar, with the same number of files and unpacked size. However, the release date for 0.19.8 is later, indicating it's a more recent build. For developers, this means the upgrade primarily involves incorporating the latest platform-specific refinements and potential patches embedded within the updated dependencies. While no groundbreaking features are introduced, staying current with the latest minor version ensures optimal compatibility and stability across diverse deployment environments. Overall, the update focuses on refining the existing excellent experience and is a worthy upgrade for projects using esbuild.
All the vulnerabilities related to the version 0.19.8 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.