Esbuild, the extremely fast JavaScript bundler and minifier, released version 0.13.5, a minor update following the previous stable version 0.13.4. Both versions maintain the same core description and licensing under the MIT license, indicating no major shifts in project direction or terms of use for developers. The repository URL also remains constant, ensuring developers can easily access the source code on GitHub.
The primary difference between the two versions lies in the version numbers of their dependencies. Both list identical sets of dependencies, covering various operating systems and architectures, including Linux (32-bit, 64-bit, ARM, ARM64, ppc64le, mips64le), SunOS (64-bit), Darwin (64-bit, ARM64), FreeBSD (64-bit, ARM64), OpenBSD (64-bit), Windows (32-bit, 64-bit, ARM64), and Android (ARM64). These dependencies, such as esbuild-linux-64, are essential platform-specific binaries that enable esbuild to function correctly on different systems. In version 0.13.5, these dependencies are updated to version 0.13.5, while in version 0.13.4, they are at version 0.13.4. This suggests that the update primarily includes bug fixes, performance improvements, or minor feature additions within the platform-specific binaries.
Developers upgrading from 0.13.4 to 0.13.5 can expect a seamless transition, as the API and core functionality are likely unchanged. The update aims to enhance the stability and efficiency of the bundler without requiring significant code modifications. The dist information also remains similar, with both versions exhibiting the same fileCount and unpackedSize, indicating a comparable distribution package. However, the releaseDate distinguishes the versions, with 0.13.5 being released on October 13, 2021, following 0.13.4's release on October 5, 2021. This highlights the incremental nature of the update.
All the vulnerabilities related to the version 0.13.5 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.