The macOS system must ignore IPv4 ICMP redirect messages.

From Apple OS X 10.13 Security Technical Implementation Guide

Associated with: CCI-000366

SV-96413r1_rule The macOS system must ignore IPv4 ICMP redirect messages.

Vulnerability discussion

ICMP redirects are broadcast to reshape network traffic. A malicious user could craft fake redirect packets and try to force all network traffic to pass through a network sniffer. If the system is not configured to ignore these packets, it could be susceptible to this kind of attack.

Check content

To check if the system is configured to ignore "ICMP redirect" messages, run the following command: sysctl net.inet.icmp.drop_redirect If the value is not "1", this is a finding.

Fix text

To configure the system to ignore "ICMP redirect" messages, add the following line to "/etc/sysctl.conf", creating the file if necessary: net.inet.icmp.drop_redirect=1

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