The macOS system must not send IPv4 ICMP redirects by default.

From Apple OS X 10.13 Security Technical Implementation Guide

Associated with: CCI-000366

SV-96419r1_rule The macOS system must not send IPv4 ICMP redirects by default.

Vulnerability discussion

ICMP redirects are broadcast to reshape network traffic. A malicious user could use the system to send fake redirect packets and try to force all network traffic to pass through a network sniffer. Disabling ICMP redirect broadcasts mitigates this risk.

Check content

To check if the system is configured to send ICMP redirects, run the following command: sysctl net.inet.ip.redirect If the values are not set to "0", this is a finding.

Fix text

To configure the system to not send ICMP redirects, add the following line to "/etc/sysctl.conf", creating the file if necessary: net.inet.ip.redirect=0

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