Esbuild version 0.6.28 marks a subtle but potentially noteworthy update to this extremely fast JavaScript bundler and minifier, following closely on the heels of version 0.6.27. While both versions share the same core description, MIT license, and repository details, a few key differences emerge upon closer inspection.
Notably, version 0.6.28, released on August 27, 2020, exhibits a slightly smaller unpacked size of 31204 bytes compared to version 0.6.27's 32114 bytes, which was released a week before on August 21, 2020. Both distributions consist of 6 files. This reduced size could indicate minor optimizations or the removal of redundant code, potentially leading to slightly faster installation and execution times.
For developers considering esbuild for their projects, the difference in unpacked size, while small, highlights the ongoing efforts to refine and optimize the tool. While detailed changelogs would provide more context behind these refinements, the reduced size points towards iterative improvements that can contribute to a smoother development experience. Consider exploring the changelogs and the official documentation for a full description of all the changes and bug fixes. Esbuild is great since it focus on performance compared to other bundlers and minifiers.
All the vulnerabilities related to the version 0.6.28 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.