Algorithmic complexity vulnerability in Moodle 1.9.x before 1.9.19, 2.0.x before 2.0.10, 2.1.x before 2.1.7, and 2.2.x before 2.2.4 allows remote authenticated users to cause a denial of service (CPU consumption) by using the advanced-search feature on a database activity that has many records.
https://exchange.xforce.ibmcloud.com/vulnerabilities/76964
http://www.securityfocus.com/bid/54481
http://secunia.com/advisories/49890