An issue was discovered in OpenStack Keystone before 15.0.1, and 16.0.0. Any authenticated user can create an EC2 credential for themselves for a project that they have a specified role on, and then perform an update to the credential user and project, allowing them to masquerade as another user. This potentially allows a malicious user to act as the admin on a project another user has the admin role on, which can effectively grant that user global admin privileges.
https://www.openwall.com/lists/oss-security/2020/05/06/5
https://usn.ubuntu.com/4480-1/
https://security.openstack.org/ossa/OSSA-2020-004.html