The Ubuntu operating system must prevent Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages from being accepted.

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Associated with: CCI-000366

SV-90559r3_rule The Ubuntu operating system must prevent Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Vulnerability discussion

Internet Control Message Protocol (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.

Check content

Verify the Ubuntu operating system will not accept IPv4 Internet Control Message Protocol (ICMP) redirect messages. Check the value of the default "accept_redirects" variables with the following command: # sudo sysctl net.ipv4.conf.default.accept_redirects net.ipv4.conf.default.accept_redirects=0 If the returned line does not have a value of "0", or a line is not returned, this is a finding.

Fix text

Configure the Ubuntu operating system to prevent Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages from being acceptedr with the following command: # sudo sysctl -w net.ipv4.conf.default.accept_redirects=0 If "0" is not the system's default value then add or update the following line in "/etc/sysctl.conf" or in the appropriate file under "/etc/sysctl.d": net.ipv4.conf.default.accept_redirects=0

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