Esbuild, the lightning-fast JavaScript bundler and minifier, saw a minor version bump from 0.1.19 to 0.1.20. While the core description remains consistent – emphasizing its speed and role as a bundler and minifier – the key difference lies in the release date. Version 0.1.20 was published on May 2nd, 2020, about nine hours after version 0.1.19 was released on May 1st, 2020.
For developers already leveraging esbuild, this update likely represents bug fixes or very minor improvements, given the short turnaround. There are no changes reflected from the description from the previous stable version such as features, or breaking changes. These releases are a great sign for the library indicating it is being maintained and improved over time.
The package maintainers have kept consistent the unpacked sizes and file count of the two versions. Though, a developer should always exercise caution before upgrading to the latest version of a library, it is suggested that this is a relatively safe upgrade.
Developers considering adopting esbuild should note its MIT license, allowing for broad usage rights. The project's repository is hosted on GitHub, making it easy to contribute or report issues, showing the package is community friendly.
All the vulnerabilities related to the version 0.1.20 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.