Esbuild version 0.3.8 is a minor update to the extremely fast JavaScript bundler and minifier, following closely on the heels of version 0.3.7. Both versions maintain the core functionality that developers appreciate: rapid build times and efficient minification for web projects. The fundamental features, MIT license, and repository details remain consistent between the two, ensuring a familiar experience for returning users.
The key difference lies in subtle refinements reflected in the dist object. Version 0.3.8 has a slightly larger unpacked size (19394 bytes) compared to 0.3.7 (19334 bytes), suggesting minor code additions, bug fixes, or performance improvements. The file count remains the same at 6 files.
The release date also marks the difference between the two versions. Version 0.3.8 was released on May 22, 2020, a day after version 0.3.7 had been released, highlighting rapid iterations during this development phase. For developers, this indicates an active project with ongoing refinements. Although the specific changes aren't detailed in the provided data, the quick release cadence implies that the updates in 0.3.8 likely address issues found in 0.3.7 or introduce small enhancements intended to further stabilize and optimize the tool. Developers should consider upgrading for potential bug fixes and performance tweaks, ensuring they are leveraging the most up-to-date version for their bundling and minification needs.
All the vulnerabilities related to the version 0.3.8 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.