The system must ignore IPv4 Internet Control Message Protocol (ICMP) redirect messages.

From Red Hat Enterprise Linux 5 Security Technical Implementation Guide

Associated with IA controls: ECSC-1

SV-37626r1_rule The system must ignore IPv4 Internet Control Message Protocol (ICMP) redirect messages.

Vulnerability discussion

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.

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Fix text

Configure the system to not accept IPv4 ICMP redirect messages. Edit /etc/sysctl.conf and add a setting for "net.ipv4.conf.all.accept_redirects=0" and "net.ipv4.conf.default.accept_redirects=0". # sysctl -p

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