Esbuild version 0.8.49 marks a slight update over its immediate predecessor, version 0.8.48. Both releases maintain the core functionality of esbuild as an exceptionally swift JavaScript bundler and minifier, licensed under MIT, continuing its mission to provide developers with a performant tool for optimizing web applications. The descriptions, licenses, and repository details remain consistent between the two versions, emphasizing the project's commitment to open-source principles, stability and ease of access through its GitHub repository.
From a developer's perspective, the minimal changes suggest a focus on incremental improvements or bug fixes rather than groundbreaking new features between these specific versions. While both versions have the same number of files and unpacked size, suggesting similar feature sets and scope, the release date is the most significant point. Version 0.8.49 was released on February 19, 2021, shortly after v0.8.48. This could indicate resolution of issues discovered in 0.8.48, or minor enhancements integrated quickly based on user feedback. Developers should review esbuild's changelog or commit history on Github around these dates for precise details on the changes, however if you are already using version 0.8.48, upgrading to version 0.8.49 is likely a safe and beneficial process.
All the vulnerabilities related to the version 0.8.49 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.