OpenStack Nova before 2012.1 allows someone with access to an EC2_ACCESS_KEY (equivalent to a username) to obtain the EC2_SECRET_KEY (equivalent to a password). Exposing the EC2_ACCESS_KEY via http or tools that allow man-in-the-middle over https could allow an attacker to easily obtain the EC2_SECRET_KEY. An attacker could also presumably brute force values for EC2_ACCESS_KEY.