Esbuild version 0.6.20 represents a minor update to the blazing-fast JavaScript bundler and minifier, following closely on the heels of version 0.6.19. Both versions share the same core characteristics: a commitment to extreme speed, a permissive MIT license, and the same repository on GitHub for open-source collaboration. In terms of size, both distributions are identical, weighing in at an unpacked size of 32153 bytes across 6 files.
The primary difference lies in the release date. Version 0.6.20 was published on August 11, 2020, while version 0.6.19 was released just a day prior, on August 10, 2020. This tight release schedule suggests that version 0.6.20 likely contains bug fixes, minor improvements, or perhaps optimizations discovered shortly after the release of 0.6.19.
For developers already using esbuild, the upgrade from 0.6.19 to 0.6.20 is likely to be seamless and worthwhile. While the change log isn't provided here, given the rapid release it would probably address edge cases or resolve build inconsistencies. Developers looking for a high-performance build tool for JavaScript and TypeScript projects should explore esbuild for significant speed improvements over traditional bundlers. Its ease of use and focus on performance make it an ideal choice for modern web development workflows. Keep in mind to double check the changelog for the specific information about the changes.
All the vulnerabilities related to the version 0.6.20 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.