Esbuild, a lightning-fast JavaScript bundler and minifier, saw a minor version update from 0.1.2 to 0.1.3 on April 13th, 2020. These versions share the same core attributes: both are released under the MIT license and hail from the same GitHub repository managed by Evan Wallace. They also feature consistent file counts and extracted sizes, indicating the fundamental architecture and core functionalities of the tools probably remained untouched.
The key difference lies in the release timing. Version 0.1.3 emerged roughly 16 minutes after 0.1.2, suggesting that the update may have addressed either minor bugs, documentation improvements, or subtle performance calibrations identified immediately after the initial release.
While the changes between these particular versions might seem incremental, Esbuild's appeal to developers stems from its impressive speed. As a bundler and minifier, Esbuild substantially cuts down the time required to prepare JavaScript code for deployment. This speed advantage can translate to faster build times during development, leading to more efficient workflows. For projects bogged down by slow build processes, adopting Esbuild, even from these early versions, may present noticeable performance boosters. Remember to always check the release notes of any package you intend to include in your project.
All the vulnerabilities related to the version 0.1.3 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.