Esbuild, a blazing-fast JavaScript bundler and minifier, released version 0.1.5 shortly after version 0.1.4, both on April 15th, 2020. While the core functionality remains consistent, with both versions offering unparalleled speed in bundling and minifying your JavaScript code, there's a notable difference in the release dates. Version 0.1.4 was released in the early morning, while 0.1.5 followed in the evening. This suggests that the later version likely addresses bugs or contains minor refinements identified after the initial 0.1.4 release.
For developers looking to integrate esbuild into their workflow, this difference, albeit subtle, is key. While the unpacked size and the number of files remain identical across both versions, opting for version 0.1.5 is advisable. It probably integrates fixes and minor upgrades. The fact that esbuild is under the MIT license and hosted on GitHub provides developers with the freedom to inspect the code, contribute improvements, and adapt the tool to their specific needs. This makes it a compelling choice for projects prioritizing performance, speed, and open-source principles in their JavaScript bundling process. The tiny unpacked size and simple structure is maintained from one version to the next. Ensure to track the changelog if upgrading from a version older than 0.1.4..
All the vulnerabilities related to the version 0.1.5 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.