Esbuild version 0.8.43 represents a subtle but tangible update over its predecessor, version 0.8.42, in the rapidly evolving landscape of JavaScript bundlers and minifiers. Both iterations maintain the core characteristics that define esbuild: blazing-fast performance, a permissive MIT license, and a commitment to efficient code transformations. Developers familiar with esbuild will find the jump from 0.8.42 to 0.8.43 seamless, as the fundamental API and underlying philosophy remain consistent.
The primary distinction lies in the details. Version 0.8.43 introduces refinements that contribute to an increased unpacked size of 69656 bytes, a slight increment from 0.8.42's 69088 bytes. The release date also separates the two versions, 0.8.43 being published on February 8th, 2021, succeeding the February 5th, 2021 release of 0.8.42. While the core functionality related to bundling and minifying remains steadfast, this increment hints at possible enhancements, bug fixes, or internal optimizations that contribute to this size increase.
For developers eyeing esbuild for their project, this upgrade signifies a continued dedication to improvement and maintaining a competitive edge in the JavaScript ecosystem. The shift might encompass enhancements to build speed, code generation efficiency, or support for emerging language features. Always refer to the project's official changelog or release notes for comprehensive details and potential migration considerations.
All the vulnerabilities related to the version 0.8.43 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.