Esbuild, a blazing-fast JavaScript bundler and minifier, saw a minor version bump from 0.1.1 to 0.1.2 in April 2020. While the core description remains consistent, highlighting its speed and functionality in bundling and minifying JavaScript code, a closer look reveals subtle differences that might be of interest to developers.
Both versions maintain the same MIT license and reside in the same GitHub repository under 'evanw/esbuild'. They share identical file structure, containing 3 files, and even have the exact same unpacked size, coming in at 2462 bytes. The key distinction lies in the release date and potentially within the code changes that prompted the version update. Version 0.1.1 was released on April 13th, 2020, at 06:45:13 UTC, while version 0.1.2 followed later the same day at 19:22:52 UTC.
For developers leveraging esbuild, this might suggest that version 0.1.2 incorporates bug fixes or minor enhancements implemented after the initial 0.1.1 release. While detailed changelogs are not provided in this data, the proximity of the releases suggests the update could address immediate issues reported by early adopters and make esbuild even more reliable, without introducing any breaking changes. Developers should check the official esbuild changelog or repository to understand the precise fixes that are released in version 0.1.2
All the vulnerabilities related to the version 0.1.2 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.