grav-plugin-api versions before 1.0.20 contain a privilege escalation vulnerability in the InvitationsController where the stripSuperFlags()

grav-plugin-api versions before 1.0.20 contain a privilege escalation vulnerability in the InvitationsController where the stripSuperFlags() method only removes nested super flags but fails to strip dot-keyed equivalents like api.super. A non-super user manager with api.access and api.users.write permissions can create an invitation with a dot-keyed super flag in the access payload that bypasses the guard and persists to the new account. Attackers can accept the invitation through the public endpoint without real invitee interaction to create a super-admin account and immediately receive a valid JWT for full site control.