Esbuild, a blazing-fast JavaScript and CSS bundler, released version 0.17.4, a minor update following closely on the heels of 0.17.3. Examining the package data, the core functionality and description remain consistent: it's still "An extremely fast JavaScript and CSS bundler and minifier." The real story lies within the dependencies and the release dates. Both versions share identical sets of both "dependencies" and "optionalDependencies", encompassing a wide array of platform-specific builds (e.g., @esbuild/linux-x64, @esbuild/darwin-arm64). The only difference within these platform specific dependencies is that version 0.17.4 depends on the 0.17.4 version of these internal packages, while version 0.17.3 depends on the 0.17.3 version of these internal packages.
The key difference between 0.17.3 and 0.17.4 is clearly its deployment window. Version 0.17.3 registered on January 18, 2023, while version 0.17.4 arrives just a few days later, on January 22, 2023. This short interval suggests that version 0.17.4 likely contains bug fixes or minor refinements addressing issues identified in 0.17.3.
For developers, the takeaway is straightforward. While a minor version bump might seem insignificant, upgrading from 0.17.3 to 0.17.4 is advisable. It potentially incorporates stability improvements and crucial patches without introducing breaking changes. Given the speed and efficiency of esbuild, staying on the latest stable release ensures optimal performance and mitigates potential risks. The file count and unpacked size are identical (7 files and 129705 unpacked size, respectively, developers can expect a seamless transition as there are no new features. The underlying esbuild architecture remains untouched, guaranteeing a smooth upgrade experience.
All the vulnerabilities related to the version 0.17.4 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.