Esbuild version 0.5.0 marks an iteration in the rapidly evolving landscape of JavaScript bundlers and minifiers, building upon the foundation laid by its predecessor, version 0.4.14. Both versions share the core characteristics of the esbuild package: lightning-fast bundling and minification capabilities, aimed at significantly reducing build times for web applications. They are both distributed under the MIT license, making them free to use in a wide range of projects, and share the same repository.
A key distinction lies in the unpacked size of the packages, with version 0.5.0 exhibiting a slightly smaller footprint (19309 bytes) compared to version 0.4.14 (20806 bytes). Though seemingly minor, this reduction could translate into faster download and installation times, especially beneficial in environments with limited bandwidth or slower storage. Developers integrating esbuild into their workflows should note the release dates: version 0.5.0 was published just hours after 0.4.14. This proximity suggests that version 0.5.0 likely addresses immediate bug fixes or minor enhancements identified shortly after the release of version 0.4.14. It is advisable for developers to upgrade to 0.5.0 to leverage these potential improvements, ensuring a smoother and more efficient bundling process without the necessity of major code changes. The upgrade promises similar performance benefits, especially for large and complex projects.
All the vulnerabilities related to the version 0.5.0 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.