Esbuild version 0.7.2, released on September 19, 2020, is a minor update to the lightning-fast JavaScript bundler and minifier, following closely on the heels of version 0.7.1 released on September 12, 2020. While seemingly similar at first glance, indicated by unchanged fileCount and unpackedSize (both 6 and 37430 respectively) these versions are differentiated by their release dates signifying underlying improvements and bug fixes of interest to developers.
For developers integrating esbuild into their workflows, this quick succession of releases suggests an active development cycle focused on stability and refinement. Choosing between 0.7.1 and 0.7.2 requires considering the fixes implemented in the later version. Upgrading to 0.7.2 is generally recommended as it offers an improved and potentially more reliable developer experience.
Esbuild, in general, is attractive for its speed, which noticeably reduces build times for web applications. Its feature set caters to modern JavaScript development, supporting ECMAScript modules, JSX, and TypeScript. By analyzing these rapid version releases, developers can gain insight into the project's commitment to creating a robust bundler, even in minor version increments, furthering esbuild's position as a solid choice for performance-conscious teams and projects.
All the vulnerabilities related to the version 0.7.2 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.