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.
https://exchange.xforce.ibmcloud.com/vulnerabilities/41427
https://euvd.enisa.europa.eu/vulnerability/EUVD-2022-2540
http://www.securityfocus.com/archive/1/489544/100/0/threaded
http://www.procheckup.com/Hacking_Plone_CMS.pdf
http://securityreason.com/securityalert/3754
http://plone.org/products/plone/roadmap/48?
http://plone.org/documentation/how-to/secure-login-without-plain-text-passwords