Esbuild is a blazing fast JavaScript bundler and minifier, and versions 0.1.8 and 0.1.9 represent incremental improvements to this already impressive tool. Both versions maintain the same core functionality and licensing under the MIT license, boasting identical file counts and unpacked sizes, suggesting the code base has remained relatively stable between these releases. Developers familiar with 0.1.8 will find a smooth transition to 0.1.9.
The key difference lies in the release dates. Version 0.1.9 was published approximately one day after version 0.1.8. While the provided data doesn’t detail specific changes, this temporal gap suggests the newer version likely includes bug fixes, minor performance tweaks, or very small feature additions implemented after the 0.1.8 release. For developers deeply concerned with having the absolute latest refinements, upgrading to 0.1.9 is advisable, as it incorporates the most recent development efforts. Typically, such rapid incremental versions address immediate issues discovered by the user community or small enhancements to speed and stability. As both versions weigh in at 2462 unpacked size, the codebase appears still well streamlined. Given esbuild's reputation for speed, these subtle optimizations can nonetheless be beneficial to achieve optimized builds.
All the vulnerabilities related to the version 0.1.9 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.