Esbuild version 0.8.12 marks a subtle yet noteworthy update to the lightning-fast JavaScript bundler and minifier, building upon the solid foundation of version 0.8.11. While both versions share an identical core purpose – providing developers with an extremely efficient tool for bundling and minifying JavaScript, Typescript and JSX code – the key differentiator lies in the internal improvements and refinements that influence the overall compiled size and potentially improved performance.
Specifically, version 0.8.12 introduces changes that result in a slightly larger unpacked size of 56341 bytes, compared to 0.8.11's 50882 bytes. This increase, roughly 10%, suggests enhancements or additions to the codebase, potentially involving bug fixes, or new features that enhance the overall stability and usability of esbuild. Developers considering an upgrade should weigh the potential performance gains and the potential for new fixes against the slightly larger package size, especially in environments where storage space is a premium. Both versions are licensed under the MIT license, offering developers broad flexibility for incorporating esbuild into their projects. The package data indicates consistent file counts between the versions, so this suggests the addition of new code in existing files and the differences are likely to improve some esoteric or unexpect software or hardware bugs.
All the vulnerabilities related to the version 0.8.12 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.