The Multi-Authentication feature in the Central Authentication Service (CAS) functionality in auth/cas/cas_form.html in Moodle 2.1.x before 2.1.6 and 2.2.x before 2.2.3 does not use HTTPS, which allows remote attackers to obtain credentials by sniffing the network.
http://openwall.com/lists/oss-security/2012/05/23/2
http://git.moodle.org/gw?p=moodle.git%3Ba=commit%3Bh=895e76ea51c462c18ad66e0761ad76cd26a63ecf