admin/roles/override.php in Moodle 2.0.x before 2.0.9, 2.1.x before 2.1.6, and 2.2.x before 2.2.3 allows remote authenticated users to gain privileges by leveraging the teacher role and modifying their own capabilities, as demonstrated by obtaining the backup:userinfo capability.
http://openwall.com/lists/oss-security/2012/05/23/2
http://git.moodle.org/gw?p=moodle.git%3Ba=commit%3Bh=0f75e1e6272db0303abc8e27362e5c3a1344b82f