Esbuild version 0.2.7 emerges as a rapid evolution of the already lightning-fast JavaScript bundler and minifier, building upon the solid foundation laid by version 0.2.6. Both versions share the same core purpose: to provide developers with an exceptionally speedy tool for bundling and minifying JavaScript code. They are released under the MIT license and hosted on GitHub, ensuring transparency and fostering community involvement.
The principal enhancements of version 0.2.7 lie subtly in the increased unpacked size, growing from 18441 to 18773, suggesting minor refinements, bug fixes, or feature additions that affect the overall footprint of the bundled package. Although the changes seem fairly minimal, the quick turnaround with a release date just hours after 0.2.6 hints at the project's active development and rapid response to potential issues or opportunities for improvement.
For developers, this implies a commitment to stability and performance. Upgrading to 0.2.7 offers the peace of mind that any unforeseen issues present in 0.2.6 may have been addressed. As esbuild is prized for its unparalleled speed, even incremental upgrades can contribute to a more efficient workflow during development and build processes. The slight increase in size is likely offset by improvements or fixes that offer tangible benefits to users, solidifying esbuild's position as a leading choice for JavaScript bundling and minification.
All the vulnerabilities related to the version 0.2.7 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.