Esbuild is a lightning-fast JavaScript bundler and minifier, and versions 0.5.21 and 0.5.20 offer developers efficient tools for optimizing their code. While both versions share the same core functionality stemming from the MIT-licensed project hosted on GitHub, a key difference lies in their specific builds. Version 0.5.21, released on July 5th, 2020, has an unpacked size of 20721 bytes, slightly larger than version 0.5.20's 20142 bytes, which came out a day earlier on July 4th, 2020.
Developers will find esbuild valuable for its speed and ease of use, particularly when dealing with complex JavaScript projects that require bundling and minification. This difference in size could indicate bug fixes, performance adjustments, or new features implemented in the newer version. For developers, this implies that upgrading to version 0.5.21 is advantageous to ensure they are working with the most refined and potentially performant iteration. The availability of both versions on npm allows for flexibility in choosing the version that best suits their project requirements. The small difference of space reflects improvements while ensuring a lightweight footprint.
All the vulnerabilities related to the version 0.5.21 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.