Rule ID
SV-257958r1155721_rule
Version
V2R8
CCIs
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. The sysctl --system command will load settings from all system configuration files. All configuration files are sorted by their filename in lexicographical 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. /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf
Verify RHEL 9 will not accept IPv4 ICMP redirect messages. Check the value of all "net.ipv4.conf.all.accept_redirects" variables with the following command: $ sudo sysctl net.ipv4.conf.all.accept_redirects net.ipv4.conf.all.accept_redirects = 0 If "net.ipv4.conf.all.accept_redirects" is not set to "0" or is missing, this is a finding.
Configure RHEL 9 to ignore IPv4 ICMP redirect messages. Create a configuration file if it does not already exist: $ sudo vi /etc/sysctl.d/99-ipv4_accept_redirects.conf Add the following line to the file: net.ipv4.conf.all.accept_redirects = 0 Reload settings from all system configuration files with the following command: $ sudo sysctl --system