Drupal, probably 5.10 and 6.4, does not set the secure flag for the session cookie in an https session, which can cause the cookie to be sent in http requests and make it easier for remote attackers to capture this cookie.
https://exchange.xforce.ibmcloud.com/vulnerabilities/45298
http://www.securityfocus.com/bid/31285
http://www.securityfocus.com/archive/1/496575/100/0/threaded