graph_realtime.php in Cacti 1.2.8 allows remote attackers to execute arbitrary OS commands via shell metacharacters in a cookie, if a guest user has the graph real-time privilege.
The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.