Snort is a widely deployed intrusion detection program.
Randy Smith, Christian Estan and Somesh Jha discovered that the rule matching algorithm of Snort can be exploited in a way known as a "backtracking attack" to perform numerous time-consuming operations.
A remote attacker could send specially crafted network packets, which would result in the cessation of the detections and the consumption of the CPU resources.
There is no known workaround at this time.
All Snort users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-analyzer/snort-2.6.1.2"