Cacti is a complete frontend to rrdtool.
The side_id parameter in data_debug.php does not properly verify input allowing SQL injection.
A remote attacker could possibly execute arbitrary code with the privileges of the process or cause a Denial of Service condition.
There is no known workaround at this time.
All Cacti users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-analyzer/cacti-1.2.16-r1"