Esbuild version 0.4.6 emerges as a quick follow-up to version 0.4.5, both iterations of a notably fast JavaScript bundler and minifier. While superficially similar, evidenced by the identical file count (6) and unpacked size (20349 bytes) in their distribution packages, a deeper look reveals a subtle but potentially impactful update. The primary difference lies in the release date: version 0.4.6 was published on June 5th, 2020, shortly after version 0.4.5's release on June 4th, 2020.
For developers considering esbuild for their projects, this rapid succession suggests a potential bug fix or minor enhancement addressed in the newer release. Individuals who adopted version 0.4.5 soon after availability should strongly evaluate migrating to version 0.4.6 to benefit from any improvements. The consistently fast bundling and minification capabilities, advertised within the shared description, still remain the core advantage. Esbuild's commitment to speed and efficient JavaScript transformation continues to make it an attractive alternative to slower bundlers, especially for larger projects where build times can significantly impact workflow. Developers should consult the official esbuild changelog or commit history on GitHub for precise insights into the changes between these versions, to make informed decision. Despite the versions being really similar the potential bug fix is a good reason to update.
All the vulnerabilities related to the version 0.4.6 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.