Esbuild version 0.9.1 represents a minor update to the blazing-fast JavaScript bundler and minifier, following closely on the heels of version 0.9.0. Both versions maintain the core promise of extreme speed and efficiency in bundling and minifying JavaScript code, licensed under the permissive MIT license. Developers familiar with 0.9.0 will find a very similar experience in 0.9.1, as the fundamental functionality remains consistent.
The key difference lies in the details. While both versions share the same file count in their distributed packages, version 0.9.1 has a slightly larger unpacked size of 70208 bytes compared to 0.9.0's 69973 bytes. This suggests that the newer version includes some minor improvements, bug fixes, or potentially expanded functionality that contribute to the increased size.
The release date also marks a clear distinction. Version 0.9.1 was released on March 12, 2021, just a few days after version 0.9.0 released on March 09, 2021. This rapid succession of releases implies that version 0.9.1 likely addresses immediate issues or enhancements identified shortly after the initial 0.9.0 release. Developers are encouraged to upgrade to 0.9.1 to benefit from these potential improvements and ensure they are using the most up-to-date and refined version of esbuild for their bundling and minification needs. As always, consult the esbuild changelog for a complete list of changes, though these minor version jumps often involve small bugfixes and performance tweaks.
All the vulnerabilities related to the version 0.9.1 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.