Payload is a free and open source headless content management system. In versions from 3.40.0 before 3.88.0 and canary versions before 4.0.0-canary.27, an attacker can craft a redirect URL parameter that sends a guest user to an untrusted destination after the authentication flow completes. This issue is fixed in versions 3.88.0 and 4.0.0-canary.27.