Esbuild, the lightning-fast JavaScript bundler and minifier, saw a relatively small update from version 0.4.3 to 0.4.4. Both versions maintain the core promise of speed and efficiency, crucial for developers looking to optimize their build processes. The package description remains consistent, emphasizing its primary function: bundling and minifying JavaScript code for faster loading times and improved performance.
The license remains MIT, providing developers with the freedom to use and modify the tool as needed. Similarly, the repository URL remains the same, pointing to the official GitHub repository for esbuild. Notably, version 0.4.4 sees a slight increase in unpacked size to 20349 bytes, compared to 20198 bytes in version 0.4.3. While seemingly insignificant, this difference could arise from minor bug fixes, performance tweaks, or small feature additions. The release date shifts from May 28, 2020, to June 3, 2020, indicating a quick turnaround between the two versions.
For developers, the key takeaway revolves around iterative enhancements. While 0.4.4 likely doesn't introduce revolutionary changes, it signifies ongoing maintenance and refinement of an already performant tool. Upgrading presents minimal risk and the potential for subtle performance gains or bug resolutions, further solidifying esbuild's value in modern JavaScript development workflows. Consider checking the official changelog (available on the GitHub repository) for a detailed breakdown of specifics.
All the vulnerabilities related to the version 0.4.4 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.