Disable Secure ICMP Redirect Acceptance Secure ICMP redirects are the same as ICMP redirects, except they come from gateways listed on the default gateway list. It is assumed that these gateways are known to your system, and that they are likely to be secure.

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It is still possible for even known gateways to be compromised. Setting net.ipv4.conf.all.secure_redirects to 0 protects the system from routing table updates by possibly compromised known gateways. Fix: Set the net.ipv4.conf.all.secure_redirects and net.ipv4.conf.default.secure_redirects parameters to 0 in /etc/sysctl.conf: net.ipv4.conf.all.secure_redirects=0 net.ipv4.conf.default.secure_redirects=0 Modify active kernel parameters to match: # /sbin/sysctl -w net.ipv4.conf.all.secure_redirects=0 # /sbin/sysctl -w net.ipv4.conf.default.secure_redirects=0 # /sbin/sysctl -w net.ipv4.route.flush=1