Esbuild is a blazing-fast JavaScript bundler and minifier, designed to significantly improve build times for web developers. Comparing versions 0.9.3 and 0.9.4, we see a small increment in unpackedSize from 70211 to 70447 bytes, suggesting minor code additions or optimizations. The release dates indicate version 0.9.4 was published on March 19, 2021, just two days after 0.9.3 (March 17, 2021), hinting at a possible quick bug fix or minor feature implementation in the newer version.
While the descriptions remain identical, developers should always prioritize the latest stable release (0.9.4 in this case) to benefit from the most up-to-date improvements and potential security patches. Although the specific changes aren't detailed in this data, upgrading from 0.9.3 to 0.9.4 is generally recommended for a more robust and performant bundling experience within your projects. The "MIT" license ensures flexibility and ease of use in various development environments. Always consult the official changelog or repository for detailed release notes to understand the specific modifications between these versions.
All the vulnerabilities related to the version 0.9.4 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.