Esbuild is a blazing-fast JavaScript bundler and minifier designed for exceptional performance. Version 0.5.13 follows closely on the heels of version 0.5.12, representing a quick iteration in the library's development. Both versions share the same core functionality, providing developers with a tool that prioritizes speed and efficiency in bundling and minifying JavaScript code for production.
The key difference lies in the release date, with version 0.5.13 being published on June 27, 2020, just a few days after version 0.5.12, released on June 24, 2020. While the unpacked size and file count remain constant, this rapid release cycle suggests that 0.5.13 likely addresses bug fixes, minor improvements, or very specific edge cases identified in the previous version. The MIT license ensures developers have broad usage rights. Developers should consider upgrading to the newer version to benefit from these potential improvements and ensure they're using the most stable and refined release of this high-performance bundler. Regularly updating to the latest point release of a library allows you to have the most up to date protection against any vulnerabilites found, and to use the most stable version of the library.
All the vulnerabilities related to the version 0.5.13 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.