A type of denial-of-service (DoS) attack that targets firewalls from a number of vendors including Cisco, Palo Alto and SonicWall was found to have resurfaced earlier this month. Unlike other DoS attacks that rely on pounding machine or network resource with large amounts of traffic, BlackNurse doesn't require much bandwidth at all. Researchers have shown that BlackNurse will work with less than 20Mbps of traffic and is effective even against large enterprise firewalls. For IT administrators who want to test for and mitigate against this kind of attack on their organisation, here are the the instructions.