Esbuild version 0.12.21 presents a subtle but potentially impactful upgrade over its predecessor, version 0.12.20. Both versions underscore esbuild's core value proposition as an exceptionally fast JavaScript bundler and minifier, ideal for developers seeking to optimize build times and reduce file sizes. Both are released under the MIT license, ensuring broad usability in various project contexts.
The key difference lies in the "unpackedSize," with v0.12.21 registering 88920 compared to v0.12.20's 88875. While the difference is small, it hints at internal adjustments or enhancements. Although the description doesn't provide verbose release notes, this shift might indicate minor bug fixes, performance tweaks, or slight alterations to the bundling algorithm. The release date also highlights the difference: v0.12.21 was released on August 18, 2021, while v0.12.20 was released just a week earlier on August 12, 2021. This short interval often signifies a rapid response to issues identified in the previous release or a targeted improvement.
Developers should consider upgrading to v0.12.21 to benefit from any potential refinements and address potential vulnerabilities. Due to the minimal nature of the change, regression risks are likely low. However, thorough testing post-upgrade is always recommended to ensure seamless integration within existing workflows. The Git repository remains consistent between versions, simplifying dependency management through standard package managers like npm or yarn.
All the vulnerabilities related to the version 0.12.21 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.