An issue was discovered in OpenStack Keystone before 15.0.1, and 16.0.0. The EC2 API doesn't have a signature TTL check for AWS Signature V4. An attacker can sniff the Authorization header, and then use it to reissue an OpenStack token an unlimited number of times.
https://www.openwall.com/lists/oss-security/2020/05/06/4
https://usn.ubuntu.com/4480-1/
https://security.openstack.org/ossa/OSSA-2020-003.html