Esbuild version 0.2.1 is a minor patch release following closely on the heels of version 0.2.0 of this blazing-fast JavaScript bundler and minifier. Both versions maintain the core functionalities that make esbuild incredibly attractive to developers: rapid build times, efficient minification, and straightforward integration into existing workflows. Crucially, the descriptions and core features remain consistent; both are described as an "extremely fast JavaScript bundler and minifier" utilizing the MIT license. The file count and unpacked size also remain static between the two versions, clocking in at 6 files and 17481 unpacked bytes respectively. The repository URL also remained static.
While the changes between 0.2.0 and 0.2.1 might appear subtle, the release date difference of a few hours on the same day indicate that version 0.2.1 likely addresses immediate bugs or critical fixes discovered shortly after the initial 0.2.0 release. For developers considering either version, prioritizing 0.2.1 is generally advisable, as it incorporates any immediate stability improvements. Think of it as receiving the most polished and refined iteration of the core 0.2 feature set. The release focuses on stability without introducing new functionality. Both rely on the same core functionalities for developers who want to use the library, rapid build times, efficient minification, and straightforward integration.
All the vulnerabilities related to the version 0.2.1 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.