Esbuild version 0.6.26 marks a subtle but important update to this incredibly fast JavaScript bundler and minifier following closely after version 0.6.25. Both versions share the same core characteristics: MIT license, identical source code repository on GitHub, the same unpacked size (32,114 bytes), and the same number of files (6) within the package. This indicates that the codebases are mostly the same
The key distinction is the release date. Version 0.6.26 was published on August 18, 2020, at 17:49:07 UTC, approximately a day and a half after version 0.6.25, which was released on August 17, 2020, at 04:06:34 UTC.
While the similar characteristics suggests that 0.6.26 is likely a patch release addressing a minor bug or issue identified in the preceding version, potentially improving stability based on user feedback. Developers using esbuild should always prioritize using the latest stable version. So, users already on 0.6.25 are advised to update to 0.6.26, potentially to resolve any hidden internal issues. The focus of esbuild remains on speed and efficiency in JavaScript bundling, attracting developers seeking faster builds and smaller bundle sizes for their web applications. This package is a powerful tool for optimizing modern web development workflows.
All the vulnerabilities related to the version 0.6.26 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.