Esbuild version 0.2.0 represents a significant update to the lightning-fast JavaScript bundler and minifier, improving upon version 0.1.26. Both versions maintain the MIT license and are accessible via the same GitHub repository. The core promise of esbuild remains true: an extremely fast and efficient tool for modern JavaScript development workflows.
However, several key distinctions separate the two versions. A primary upgrade is the notable increase in unpackedSize, jumping from 9534 bytes in version 0.1.26 to 17481 bytes in version 0.2.0. This nearly doubles the size of the library which could indicates new features, optimizations, or increased file sizes of binaries packaged within. For developers, the increased unpackedSize might imply improved capabilities and performance enhancements.
The release date also distinguishes the two. Version 0.2.0 was released on May 5th, 2020, later the same day that version 0.1.26 was released. Developers might be interested in exploring the changelog or release notes for version 0.2.0 to fully understand the implications of the size increase and to determine if the changes warrant an upgrade for their projects. The quick release succession suggests a bug fix or a fast follow up functionality released on top of the previous one.
All the vulnerabilities related to the version 0.2.0 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.