Esbuild is a blazing-fast JavaScript bundler and minifier, and versions 0.5.3 and 0.5.4 showcase its rapid development cycle. While the core functionality remains consistent between these releases, examining their differences highlights the ongoing improvements developers can expect.
Both versions share identical descriptions, license (MIT), repository details, file count (6), and unpacked size (19309 bytes), meaning the core package structure and size didn't change visibly between releases. The significant difference lies entirely in the release date. Version 0.5.4 was released on June 19, 2020, while version 0.5.3 was released a week earlier on June 12, 2020.
For developers, the weekly release cadence suggests an active project with frequent bug fixes and potentially minor feature enhancements that are important to follow. While it's impossible to determine the exact features added in 0.5.4 without additional release notes, the existence of a new version indicates that bug fixes or small improvements were sufficient to warrant a new version. For users considering adopting esbuild, this data suggests a project where issues are often addressed quickly, and developers must assess the changelogs to evaluate if the new version contains breaking changes or important fixes. This rapid iteration is a positive sign for long-term maintainability and a vibrant developer community.
All the vulnerabilities related to the version 0.5.4 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.