Esbuild version 0.5.20 follows closely on the heels of version 0.5.19, both maintaining the core promise of an extremely fast JavaScript bundler and minifier. Crucially, while the fileCount and unpackedSize remain identical between the two versions (6 files and 20142 bytes, respectively, suggesting no substantial changes to the core architecture or delivered asset size), the release dates signal a minor but potentially significant update. Version 0.5.20 was released on July 4th, 2020, just under two days after version 0.5.19's release on July 2nd, 2020.
For developers, this quick turnaround implies that 0.5.20 likely addresses bug fixes, performance tweaks, or very minor feature enhancements detected shortly after the previous release. While the changelog for these specific versions should be consulted for precise details, developers already using esbuild in their projects benefit from upgrading to 0.5.20. This is because any bug fixes or performance gains included will incrementally improve their build processes. New users can confidently begin with the slightly newer version. The consistent file size suggests the core API and usage patterns remain stable. As a result, learning resources for earlier 0.5.x versions remain relevant.
All the vulnerabilities related to the version 0.5.20 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.