Level 1 - Server Level 1 - Workstation
ICMP Redirects are used to send routing information to other hosts. As a host itself does not act as a router (in a host only configuration), there is no need to send redirects.
An attacker could use a compromised host to send invalid ICMP redirects to other router devices in an attempt to corrupt routing and have users access a system set up by the attacker as opposed to a valid system.
Run the following command and verify output matches:
# sysctl net.ipv4.conf.all.send_redirects net.ipv4.conf.all.send_redirects = 0 # sysctl net.ipv4.conf.default.send_redirects net.ipv4.conf.default.send_redirects = 0
Set the following parameter in the “/etc/sysctl.conf” file:
net.ipv4.conf.all.send_redirects = 0 net.ipv4.conf.default.send_redirects = 0
Run the following commands to set the active kernel parameters:
# sysctl -w net.ipv4.conf.all.send_redirects=0 # sysctl -w net.ipv4.conf.default.send_redirects=0 # sysctl -w net.ipv4.route.flush=1