Esbuild version 0.19.9 represents a minor update over its predecessor, version 0.19.8, within the esbuild ecosystem, a JavaScript and CSS bundler renowned for its exceptional speed. Examining the package data, the core description remains consistent: it is still advertised as an extremely fast bundler and minifier. The key differences lie primarily in the versioning of its dependencies and the release date. Both versions share an identical set of dependencies and optional dependencies, each tailored to specific operating systems and architectures, ranging from Linux and Windows to macOS and Android, supporting a wide array of processor architectures including x64, ARM, and others. The dependencies versions are aligned with the package version itself, moving from 0.19.8 to 0.19.9. While the core functionality is likely unchanged, this update ensures compatibility and potentially incorporates bug fixes or performance improvements within those underlying platform-specific packages. The release date difference indicates that version 0.19.9 was published more recently, on December 10, 2023, compared to version 0.19.8, released on November 26, 2023. Developers should consider updating to the latest version to benefit from the most recent fixes and optimizations, even if the changes appear incremental. The fileCount and unpackedSize remain identical between the versions.
All the vulnerabilities related to the version 0.19.9 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.