OL08-00-040210 - OL 8 must prevent IPv6 Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Information

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 lexicographic order, regardless of which of the directories they reside in. 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

Solution

Configure OL 8 to prevent IPv6 ICMP redirect messages from being accepted with the following command:

$ sudo sysctl -w net.ipv6.conf.default.accept_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

If '0' is not the system's default value, add or update the following line in '/etc/sysctl.conf' or in the appropriate file under '/etc/sysctl.d':

net.ipv6.conf.default.accept_redirects=0

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Oracle_Linux_8_V2R2_STIG.zip

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6b., CAT|II, CCI|CCI-000366, Rule-ID|SV-248876r991589_rule, STIG-ID|OL08-00-040210, Vuln-ID|V-248876

Plugin: Unix

Control ID: 7508b2d018917ac1514c13a6b637d223a7b62a601aed3ef4190d05bebd793da4