Black Nurse DOS attack
Blacknurse is a low bandwidth ICMP attack that is capable of doing denial of service to well known firewalls. Most ICMP attacks that we see are based on ICMP Type 8 Code 0 also called a ping flood attack. BlackNurse is based on ICMP with Type 3 Code 3 packets. We know that when a user has allowed ICMP Type 3 Code 3 to outside interfaces, the BlackNurse attack becomes highly effective even at low bandwidth. Low bandwidth is in this case around 15-18 Mbit/s. This is to achieve the volume of packets needed which is around 40 to 50K packets per second. It does not matter if you have a 1 Gbit/s Internet connection. The impact we see on different firewalls is typically high CPU loads. When an attack is ongoing, users from the LAN side will no longer be able to send/receive traffic to/from the Internet. All firewalls we have seen recover when the attack stops.
To mitigate this attack on Cisco routers the following commands can help
icmp deny any unreachable outside
icmp deny any time outside
gcc exploit.c -o blacknurse
./blacknurse <target ip>
apt-get install python-scapy
pip install scapy
This code was based on a Perl implementation of this attack by Todor Donev and this flaw was discovered by Kenneth B. Jørgensen and Lenny Hansson, thanks guys !
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