ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.
The sysctl --system command will load settings from all system configuration files. All configuration files are sorted by their filename in lexicographic order, regardless of the directories in which they reside. If multiple files specify the same option, the entry in the file with the lexicographically latest name will take precedence. Files are read from directories in the following list from top to bottom. Once a file of a given filename is loaded, any file of the same name in subsequent directories is ignored.
If "net.ipv4.conf.all.send_redirects" is not set to "0", is missing or commented out, this is a finding.
If conflicting results are returned, this is a finding.
Fix
Configure RHEL 9 to not allow interfaces to perform IPv4 ICMP redirects.
Add or edit the following line in a system configuration file in the "/etc/sysctl.d/" directory:
net.ipv4.conf.all.send_redirects=0
Remove any configurations that conflict with the above from the following locations: /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf /etc/sysctl.d/*.conf
Load settings from all system configuration files with the following command: