Esbuild version 0.8.52 represents a minor update following version 0.8.51, both iterations building upon the core promise of an extremely fast JavaScript bundler and minifier. Both versions share the same MIT license, hosted repository, and overall purpose. Examining the technical specifications, the core difference lies within the dist metadata. Version 0.8.52 exhibits a slightly larger unpackedSize of 71470 bytes compared to version 0.8.51's 71344 bytes, a difference of 126 bytes. The file count remains consistent at 6 files for both versions, suggesting any changes were likely within existing files rather than the addition of new ones. Significantly, the release dates differ, with version 0.8.52 being published on February 25, 2021, after version 0.8.51 published on the 23rd.
For developers considering integrating esbuild into their workflow, this increment signifies a refinement of the existing capabilities or a targeted bug fix. Given the small increment in size, it's plausible that the update addresses a specific edge case or introduces micro-optimizations, without revolutionary changes. Before upgrading, developers using 0.8.51 should weigh whether the advantages of possibly getting bug fixes are more important than the risk of introducing new issues. Consult the official changelog or commit history on esbuild's GitHub repository for a more fine-grained understanding of the changes introduced in 0.8.52. Developers can continue leveraging esbuild for its speed and efficiency in bundling and minifying JavaScript, achieving faster build times and smaller bundle sizes in their JavaScript projects.
All the vulnerabilities related to the version 0.8.52 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.