Esbuild, a lightning-fast JavaScript bundler and minifier, released version 0.3.1 shortly after version 0.3.0. Both share identical descriptions, being hailed for their extreme speed in bundling and minifying JavaScript code, beneficial for developers aiming to optimize website performance and reduce load times. Both are licensed under the permissive MIT license and their code is hosted on GitHub, allowing for open contributions and easy access for developers. The distribution details are also surprisingly identical: both versions contain 6 files when packaged and unpack to a size of 18773 bytes.
The primary difference lies in the release date. Version 0.3.0 was released on May 13, 2020, while version 0.3.1 followed on May 14, 2020, indicating a very quick turnaround. Developers should investigate the specific commit history between these two versions as there are likely important bug fixes or minor improvements between the two versions. Because the sizes are identical, the changes are likely constrained to just a few files.
For developers considering integrating esbuild into their workflow, the choice between 0.3.0 and 0.3.1 depends on the specific issues addressed in the latter. Reviewing the change logs to understand these subtle changes is recommended to determine the most suitable version for their specific project, and may allow developers to avoid previously encountered bugs.
All the vulnerabilities related to the version 0.3.1 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.