RHEL 8 must not respond to Internet Control Message Protocol (ICMP) echoes sent to a broadcast address.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230537	RHEL-08-040230	SV-230537r792942_rule		Medium

Description
Responding to broadcast ICMP echoes facilitates network mapping and provides a vector for amplification attacks. There are notable differences between Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). IPv6 does not implement the same method of broadcast as IPv4. Instead, IPv6 uses multicast addressing to the all-hosts multicast group. Refer to RFC4294 for an explanation of "IPv6 Node Requirements", which resulted in this difference between IPv4 and IPv6. 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

Responding to broadcast ICMP echoes facilitates network mapping and provides a vector for amplification attacks. There are notable differences between Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6). IPv6 does not implement the same method of broadcast as IPv4. Instead, IPv6 uses multicast addressing to the all-hosts multicast group. Refer to RFC4294 for an explanation of "IPv6 Node Requirements", which resulted in this difference between IPv4 and IPv6. 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-33206r792940_chk )
Verify RHEL 8 does not respond to ICMP echoes sent to a broadcast address. Note: If IPv4 is disabled on the system, this requirement is Not Applicable. Check the value of the "icmp_echo_ignore_broadcasts" variable with the following command: $ sudo sysctl net.ipv4.icmp_echo_ignore_broadcasts net.ipv4.icmp_echo_ignore_broadcasts = 1 If the returned line does not have a value of "1", a line is not returned, or the retuned line is commented out, this is a finding. Check that the configuration files are present to enable this network parameter. $ sudo grep -r net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.d/*.conf /etc/sysctl.d/99-sysctl.conf: net.ipv4.icmp_echo_ignore_broadcasts = 1 If "net.ipv4.icmp_echo_ignore_broadcasts" is not set to "1", 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-33206r792940_chk )

Verify RHEL 8 does not respond to ICMP echoes sent to a broadcast address.

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

Check the value of the "icmp_echo_ignore_broadcasts" variable with the following command:

$ sudo sysctl net.ipv4.icmp_echo_ignore_broadcasts

net.ipv4.icmp_echo_ignore_broadcasts = 1

If the returned line does not have a value of "1", a line is not returned, or the retuned line is commented out, this is a finding.

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

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

/etc/sysctl.d/99-sysctl.conf: net.ipv4.icmp_echo_ignore_broadcasts = 1

If "net.ipv4.icmp_echo_ignore_broadcasts" is not set to "1", 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-33181r792941_fix)
Configure RHEL 8 to not respond to IPv4 ICMP echoes sent to a broadcast address. Add or edit the following line in a system configuration file, which begins with "99-", in the "/etc/sysctl.d/" directory: net.ipv4.icmp_echo_ignore_broadcasts=1 Load settings from all system configuration files with the following command: $ sudo sysctl --system