Esbuild versions 0.8.28 and 0.8.27 represent incremental updates to this exceptionally fast JavaScript bundler and minifier. Both versions maintain the same core description and licensing – indicating stability in the project's foundation and continued commitment to the MIT license. The fundamental aspects, such as the project's repository on GitHub and the number of files included within the package remain identical too. However, examining the timestamps provided reveals a key difference: version 0.8.28 was released on December 31, 2020, while 0.8.27 was released a few days earlier, on December 29, 2020.
While the unpacked size hasn't changed, this time difference suggests that 0.8.28 likely incorporates bug fixes, performance enhancements, or minor feature adjustments implemented after the release of 0.8.27. For developers using esbuild, upgrading to the latest version (0.8.28) is generally recommended to benefit from these improvements, ensure compatibility with recent changes in the JavaScript ecosystem, and address potential security vulnerabilities. Keep in mind that the impact of those changes vary greatly based on the code bundled. To assess the real impact a comparison to the changelogs should be done. Considering Esbuild's focus on speed, even small optimizations are relevant for projects where build times are critical.
All the vulnerabilities related to the version 0.8.28 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.