Esbuild version 0.9.5 introduces subtle yet potentially important refinements over its predecessor, version 0.9.4. Both versions maintain the core functionality that has made esbuild a popular choice: extremely fast JavaScript bundling and minification. This efficiency stems from its use of Go, enabling significantly quicker build times compared to JavaScript-based bundlers. Developers benefit from rapid feedback loops, critical for iterative development and faster deployment cycles.
While the descriptions, license (MIT), and repository details remain identical across both versions, the key difference lies in the release date. Version 0.9.5 was published on March 19, 2021, at 18:05:28.758Z, while version 0.9.4 was released earlier the same day at 05:56:25.790Z. Although the fileCount (6) and unpackedSize (70447) are identical suggesting no major code changes, the later release of 0.9.5 implies potential bug fixes or minor enhancements implemented after the 0.9.4 release. For developers, particularly those working on critical projects, upgrading to version 0.9.5 even if it seems like a small patch is advisable to ensure they are using the most up-to-date and stable iteration. The consistent tarball naming convention reflects the unchanged file structure and simplifies version management. Both versions offer a lightweight and performant solution for bundling, attractive for projects prioritizing build speed and minimized bundle sizes.
All the vulnerabilities related to the version 0.9.5 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.