Esbuild version 0.9.7 arrives as a small but potentially impactful update to the blazing-fast JavaScript bundler and minifier. Released on March 24, 2021, it closely follows version 0.9.6, which was released just a few days prior on March 20, 2021. Both versions share the same core description, license (MIT), and repository details, underscoring the project's commitment to open-source principles and consistent branding.
The key differentiators lie in the internal details. While both tarballs contain 6 files, version 0.9.7 shows a slight increase in unpacked size, going from 75,405 bytes in 0.9.6 to 75,618 bytes. This 213-byte difference suggests that the new release includes some minor fixes or small feature additions impacting the overall "footprint" of the library.
For developers, this means a possible improvement in performance or the resolution of smaller, previously existing bugs. While the change might seem insignificant at first glance, these small increments can be meaningful in the long run, particularly for larger projects or those that rely on esbuild's efficient code generation. The quick release cadence indicates that the esbuild team is actively addressing feedback and refining the library. Upgrading to version 0.9.7 is recommendable for projects already using esbuild and is a good starting point for new users.
All the vulnerabilities related to the version 0.9.7 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.