RHEL 8 must not enable IPv4 packet forwarding unless the system is a router.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-250317	RHEL-08-040259	SV-250317r793008_rule		Medium

Description
Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this software is used when not required, system network information may be unnecessarily transmitted across the network. 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 Based on the information above, if a configuration file that begins with "99-" is created in the "/etc/sysctl.d/" directory, it will take precedence over any other configuration file on the system.

Description

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this software is used when not required, system network information may be unnecessarily transmitted across the network. 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 Based on the information above, if a configuration file that begins with "99-" is created in the "/etc/sysctl.d/" directory, it will take precedence over any other configuration file on the system.

STIG	Date
Red Hat Enterprise Linux 8 Security Technical Implementation Guide	2021-12-03

Details

Check Text ( C-53751r793006_chk )
Verify RHEL 8 is not performing IPv4 packet forwarding, unless the system is a router. Note: If IPv4 is disabled on the system, this requirement is Not Applicable. Check that IPv4 forwarding is disabled using the following command: $ sudo sysctl net.ipv4.ip_forward net.ipv4.ip_forward = 0 If the IPv4 forwarding value is not "0" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding. Check that the configuration files are present to enable this network parameter. $ sudo grep -r net.ipv4.conf.all.forwarding /etc/sysctl.d/*.conf /etc/sysctl.d/99-sysctl.conf: net.ipv4.conf.all.forwarding = 0 If "net.ipv4.conf.all.forwarding" is not set to "0", is missing or commented out, this is a finding. If the configuration file does not begin with "99-", this is a finding.

Check Text ( C-53751r793006_chk )

Verify RHEL 8 is not performing IPv4 packet forwarding, unless the system is a router.

Note: If IPv4 is disabled on the system, this requirement is Not Applicable.

Check that IPv4 forwarding is disabled using the following command:

$ sudo sysctl net.ipv4.ip_forward

net.ipv4.ip_forward = 0
If the IPv4 forwarding value is not "0" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, this is a finding.

Check that the configuration files are present to enable this network parameter.

$ sudo grep -r net.ipv4.conf.all.forwarding /etc/sysctl.d/*.conf

/etc/sysctl.d/99-sysctl.conf: net.ipv4.conf.all.forwarding = 0

If "net.ipv4.conf.all.forwarding" is not set to "0", is missing or commented out, this is a finding.

If the configuration file does not begin with "99-", this is a finding.

Fix Text (F-53705r793007_fix)
Configure RHEL 8 to not allow IPv4 packet forwarding, unless the system is a router. Add or edit the following line in a system configuration file, which begins with "99-", in the "/etc/sysctl.d/" directory: net.ipv4.conf.all.forwarding=0 Load settings from all system configuration files with the following command: $ sudo sysctl --system