Magento versions 2.4.1 (and earlier), 2.4.0-p1 (and earlier) and 2.3.6 (and earlier) are vulnerable to an insecure direct object vulnerability (IDOR) in the customer API module. Successful exploitation could lead to sensitive information disclosure and update arbitrary information on another user's account.
https://helpx.adobe.com/security/products/magento/apsb21-08.html