Esbuild, a blazing-fast JavaScript bundler and minifier, saw a subtle update with the release of version 0.6.16 following closely on the heels of version 0.6.15. Both versions, licensed under MIT, share the same core description: delivering exceptional speed in bundling and minifying JavaScript code. They also maintain identical repository information, pointing to the official GitHub repository for esbuild. Despite having the same description, maintainer and repository there is a small time difference on the release date.
Developers considering esbuild for their projects will be pleased to note that both versions 0.6.15 and 0.6.16 have the same file count (6) and unpacked size (29538 bytes). This suggests that the changes between the releases are relatively minor, likely focusing on bug fixes, performance tweaks, or small feature enhancements. The key difference lies in the release date, with version 0.6.16 being released shortly after version 0.6.15, suggesting a really quick fix or patch.
For developers, this quick turnaround is important. If you are using version 0.6.15, upgrading to 0.6.16 looks like a good and easy choice. While details of the exact changes aren't included in the data provided, such a rapid update usually signals a worthwhile enhancement for stability or reliability.
All the vulnerabilities related to the version 0.6.16 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.