Esbuild version 0.8.45 represents a subtle but potentially important update to the popular JavaScript bundler and minifier. Building upon the foundation of version 0.8.44, this release, published on February 13, 2021, continues to offer developers an extremely fast and efficient tool for optimizing their JavaScript code. Esbuild's core value proposition remains unchanged: providing blazing-fast build times compared to other bundlers, enabling quicker development cycles and improved productivity.
While the core feature set remains consistent, the key difference lies in the updated unpacked size, now at 71,765 bytes compared to 0.8.44's 71,605 bytes. This slight increase suggests internal improvements, bug fixes, or potentially feature enhancements implemented within the codebase. Although not explicitly stated in the provided data, developers can anticipate that version 0.8.45 builds upon the stability and performance of the previous release, addressing any known issues and further refining the bundling and minification process. For developers already using esbuild, upgrading to version 0.8.45 is likely a safe and recommended practice to benefit from the latest refinements and ensure compatibility. New users will find in esbuild one of the fastest JavaScript bundlers available on the market. Choosing the newest version guarantee all the fixes and improvements from the authors.
All the vulnerabilities related to the version 0.8.45 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.