Esbuild, an exceptionally fast JavaScript bundler and minifier, saw a minor version update from 0.2.2 to 0.2.3 on May 6th, 2020. While the core functionality described in the package's description remains consistent – offering developers a swift solution for bundling and minifying their JavaScript code – digging deeper reveals subtle differences.
Both versions are licensed under the MIT license, ensuring broad compatibility and freedom for developers to integrate esbuild into their projects. They also share the same code repository on GitHub, indicating a common development lineage. The fileCount and unpackedSize attributes within the dist object are identical, suggesting that the raw size and number of files within the distributed package remained unchanged between versions.
The most salient difference lies in the releaseDate. Version 0.2.3 was published approximately two hours after version 0.2.2. This suggests that the update likely contained bug fixes or minor improvements implemented shortly after the initial 0.2.2 release. For developers already using esbuild, upgrading from 0.2.2 to 0.2.3 likely involved minimal effort and offered a potentially more stable and refined experience.
For developers seeking a speedy and efficient JavaScript bundler, esbuild remains an attractive option. The extremely fast bundling and minification capabilities can significantly reduce build times and improve website performance. Although the difference between versions 0.2.2 and 0.2.3 appears minor, keeping up with the latest releases is generally advisable to benefit from the most up-to-date fixes and refinements.
All the vulnerabilities related to the version 0.2.3 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.