Esbuild version 0.3.7 offers a subtle but noteworthy update over its predecessor, version 0.3.6. Both versions maintain the core promise of being an extremely fast JavaScript bundler and minifier, adhering to the MIT license and originating from the same GitHub repository managed by Evan Wallace. Developers can leverage esbuild for blazing-fast build times, significantly improving development workflows, especially in large projects. The key difference lies in the unpacked size, which slightly increases from 19025 bytes in version 0.3.6 to 19334 bytes in version 0.3.7, implying refinements and potentially minor feature additions or bug fixes.
The release dates also highlight a close succession, with 0.3.6 appearing on May 21, 2020, at 06:50:54 UTC and 0.3.7 later the same day at 20:40:48 UTC. This rapid release suggests a hotfix or a small but important enhancement was deemed necessary. Both versions ship with a file count of 6 in their respective tarballs. Developers should consider upgrading from 0.3.6 to 0.3.7 to benefit from the latest stability improvements and potential performance optimizations embedded within the slightly larger package size. While the changelog isn't explicit, the update encourages users to stay current with the rapidly evolving esbuild ecosystem. Choosing esbuild means opting for a modern tool optimized for speed and efficiency in JavaScript bundling and minification.
All the vulnerabilities related to the version 0.3.7 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.