CVE-2008-1393
Plone CMS 3.0.5, and probably other 3.x versions, places a base64 encoded form of the username and password in the __ac cookie for the admin account, which makes it easier for remote attackers to obtain administrative privileges by sniffing the network.
Date published : 2008-03-19
http://www.securityfocus.com/archive/1/489544/100/0/threaded
http://plone.org/documentation/how-to/secure-login-without-plain-text-passwords