Esbuild version 0.2.12 represents a minor update over its predecessor, version 0.2.11, in the fast-paced world of JavaScript bundling. While the core functionality of this exceptionally quick bundler and minifier remains consistent, developers should note the subtle improvements and fixes introduced in this iteration. Both versions share the same foundational attributes: an MIT license, a GitHub repository managed by Evan Wallace, and a compact distribution footprint of 6 files, unpacking to 18774 bytes.
The key difference lies in the release date, with version 0.2.12 appearing on May 13, 2020, a few days after the May 10, 2020 release of version 0.2.11. This suggests that version 0.2.12 likely incorporates bug fixes, performance enhancements, or relatively minor feature additions identified and addressed shortly after the previous release. For developers already using esbuild, upgrading to 0.2.12 ensures they benefit from the latest refinements and stability improvements.
New users should always opt for the most recent version, as it represents the most polished and optimized experience. Given esbuild's focus on speed and efficiency, even incremental improvements are beneficial, streamlining the build process and reducing development time. Esbuild remains a compelling choice for projects prioritizing rapid bundling and minification, offering a significant edge in modern JavaScript workflows.
All the vulnerabilities related to the version 0.2.12 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.