CVE 2014-5277

Docker before 1.3.1 and docker-py before 0.5.3 fall back to HTTP when the HTTPS connection to the registry fails, which allows man-in-the-middle attackers to conduct downgrade attacks and obtain authentication and image data by leveraging a network position between the client and the registry to block HTTPS traffic.

See the CVE page on Mitre.org for more details.