Esbuild, the blazing-fast JavaScript bundler and minifier, saw a minor version bump from 0.6.17 to 0.6.18 in early August 2020. While both versions share the same core characteristics – MIT licensing, a GitHub repository managed by Evan Wallace, and a streamlined package structure – subtle improvements were introduced.
Developers considering an upgrade will find that version 0.6.18 delivers a refined experience. While the core functionality remains consistent, the unpacked size of the package increased slightly, suggesting internal code enhancements or bug fixes potentially affecting performance or stability. The unpackedSize grew from 31,022 bytes in 0.6.17 to 32,153 bytes in 0.6.18. Though seemingly small, such a change often signals behind-the-scenes optimizations.
The release date difference indicates a rapid iteration cycle, with 0.6.18 arriving just two days after 0.6.17. This suggests a responsive development team actively addressing issues and delivering incremental improvements. Developers prioritizing the latest enhancements and potential bug fixes would benefit from upgrading to version 0.6.18. As always, thorough testing in a development environment is recommended before deploying to production to ensure seamless integration with your existing project. Both versions promise unparalleled speed when bundling and minifying JavaScript, making esbuild a worthwhile consideration for any performance-conscious web developer.
All the vulnerabilities related to the version 0.6.18 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.