Title

The Ubuntu operating system must ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages. (Cat II impact)

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 ignores Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages. Check the value of the "accept_redirects" variables with the following command: # sudo sysctl net.ipv4.conf.all.accept_redirects net.ipv4.conf.all.accept_redirects=0 If both of the returned lines do not have a value of "0", or a line is not returned, this is a finding.

Fix Text

Configure the Ubuntu operating system to ignore Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirect messages with the following command: # sudo sysctl -w net.ipv4.conf.all.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.all.accept_redirects=0

Additional Identifiers

Rule ID: SV-215150r610931_rule

Vulnerability ID: V-215150

Group Title: SRG-OS-000480-GPOS-00227

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