zabbix_agentd in Zabbix before 1.8.6 and 1.9.x before 1.9.4 allows context-dependent attackers to cause a denial of service (CPU consumption) by executing the vfs.file.cksum command for a special device, as demonstrated by the /dev/urandom device.
http://www.zabbix.com/rn1.8.6.php