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.

References

• https://nvd.nist.gov/vuln/detail/CVE-2014-5277
• moby/moby@8caacb1
• https://groups.google.com/forum/#!topic/docker-user/oYm0i3xShJU
• https://groups.google.com/forum/#%21topic/docker-user/oYm0i3xShJU
• https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-5277
• http://lists.opensuse.org/opensuse-updates/2014-11/msg00048.html