Esbuild version 0.8.39 represents a minor update over its predecessor, version 0.8.38, in the rapidly evolving JavaScript bundler landscape. While both versions share the same core characteristics of being an extremely fast JavaScript bundler and minifier under the MIT license, a few subtle differences could be of interest to developers.
The key difference lies in the release date. Version 0.8.39 was published on February 1, 2021, while version 0.8.38 was released the day before, January 31, 2021. This suggests that v0.8.39 likely includes bug fixes, performance tweaks, or minor feature adjustments introduced in the short timeframe between the two releases. Although the core functionality remains consistent, developers might find v0.8.39 to offer a slightly more refined and stable experience.
Furthermore, the "unpackedSize" in the distribution metadata reveal a minor size difference. v0.8.39 occupies 68320 bytes when unpacked, compared to 69309 bytes for v0.8.38. This reduction in size, though small, could indicate optimizations in the code or the removal of redundant elements, potentially resulting in slightly faster load times or reduced memory footprint when using the bundler.
For developers considering Esbuild, both versions highlight its key strengths: speed and efficiency. Esbuild is renowned for its significantly faster bundling and minification compared to other tools in the ecosystem. It's a compelling choice for projects where build times are critical, especially large and complex applications. Updating to the latest minor version(0.8.39) is also recommended to ensure you're benefiting from the latest improvements.
All the vulnerabilities related to the version 0.8.39 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.