Esbuild has released version 0.20.0, updating from the previous stable version 0.19.12. Both versions are described as extremely fast JavaScript and CSS bundlers and minifiers designed to streamline development workflows. A notable difference lies in the optional dependencies, each version aligning these with their respective version number for platform-specific builds. Both versions include optional dependencies like @esbuild/linux-x64, @esbuild/win32-x64, @esbuild/darwin-x64 and others, catering to diverse operating systems and architectures, ensuring optimal performance across different environments. Developers can leverage these platform-specific packages for targeted deployments.
The unpacked size has slightly increased from 133,381 bytes in version 0.19.12 to 133,669 bytes in version 0.20.0, suggesting minor additions or modifications to the core library. The fileCount remains constant at 7. The release date for version 0.20.0 is January 27, 2024, while version 0.19.12 was released on January 23, 2024, indicating a relatively short period between releases. Developers planning to update should consider the minor increase in size and review the changelog for detailed information on bug fixes, performance improvements, and new features introduced in version 0.20.0 to ensure compatibility and optimal usage within their projects. Esbuild is still under the MIT license, and hosted under the same git repository.
All the vulnerabilities related to the version 0.20.0 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.