Esbuild version 0.9.3 is a minor release following version 0.9.2 of this exceptionally fast JavaScript bundler and minifier. Both versions maintain the same core description and MIT license, affirming their commitment to providing developers with a performant and freely usable tool. The source code repository remains consistent, hosted on GitHub under the evanw/esbuild project.
While seemingly incremental, the differences between the two versions offer subtle improvements for developers. Most notably, version 0.9.3, released on March 17, 2021, boasts a slightly larger unpacked size of 70211 bytes, compared to version 0.9.2's 70208 bytes. This suggests the inclusion of potentially minor enhancements, bug fixes, or new features that contribute to the overall package size.
Given esbuild's reputation for speed and efficiency, even small changes can impact build times and bundle sizes. Developers should consider upgrading to version 0.9.3 to take advantage of these potential improvements. The tarball URL in the npm registry points to where developers can download version 0.9.3, while version 0.9.2 was released 5 days before. This tool remains a valuable asset for optimizing JavaScript projects, and staying updated with the latest minor releases ensures developers benefit from the ongoing refinements. It is important to check official release notes to fully understand what those few bytes more brought to the tool.
All the vulnerabilities related to the version 0.9.3 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.