Esbuild is a blazing-fast JavaScript and CSS bundler and minifier, designed to supercharge your web development workflow. Comparing versions 0.18.3 and 0.18.4 reveals a subtle but important upgrade. While both versions share identical descriptions, dependencies (including platform-specific packages for various operating systems and architectures like Linux, Windows, macOS, Android, and FreeBSD), optional dependencies and the same unpacked size of 130436, the key difference lies in the version numbers of their included dependencies and the timing of their releases. Version 0.18.4 upgrades all @esbuild/* dependencies to version 0.18.4 from version 0.18.3 and was released on June 16, 2023, whereas version 0.18.3 was cut on June 15, 2023.
For developers, this signifies a refinement in the build process, potentially addressing bugs or performance bottlenecks present in the earlier release. Although the changes might appear incremental, using the latest version (0.18.4) ensures you're benefiting from the most current optimizations and fixes. Esbuild's architecture, evident in its platform-specific dependency structure, allows for optimized performance across diverse environments. The MIT license and accessible Git repository provide transparency and contribute to its appeal for a wide range of projects, from small web apps to large-scale enterprise applications. Choosing version 0.18.4 means getting the freshest iteration of this powerful tool with any bug fixes or optimizations it offers.
All the vulnerabilities related to the version 0.18.4 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.