RHEL 9 must be configured to use TCP syncookies.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257957	RHEL-09-253010	SV-257957r991589_rule		Medium

Description
Denial of service (DoS) is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity. Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning. Satisfies: SRG-OS-000480-GPOS-00227, SRG-OS-000420-GPOS-00186, SRG-OS-000142-GPOS-00071

Description

Denial of service (DoS) is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity. Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning. Satisfies: SRG-OS-000480-GPOS-00227, SRG-OS-000420-GPOS-00186, SRG-OS-000142-GPOS-00071

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2024-06-04

Details

Check Text ( C-61698r942982_chk )
Verify RHEL 9 is configured to use IPv4 TCP syncookies. Determine if syncookies are used with the following command: Check the status of the kernel.perf_event_paranoid kernel parameter. $ sudo sysctl net.ipv4.tcp_syncookies net.ipv4.tcp_syncookies = 1 Check that the configuration files are present to enable this kernel parameter. $ sudo /usr/lib/systemd/systemd-sysctl --cat-config \| egrep -v '^(#\|;)' \| grep -F net.ipv4.tcp_syncookies \| tail -1 net.ipv4.tcp_syncookies = 1 If the network parameter "ipv4.tcp_syncookies" is not equal to "1" or nothing is returned, this is a finding.

Check Text ( C-61698r942982_chk )

Verify RHEL 9 is configured to use IPv4 TCP syncookies.

Determine if syncookies are used with the following command:

Check the status of the kernel.perf_event_paranoid kernel parameter.

$ sudo sysctl net.ipv4.tcp_syncookies

net.ipv4.tcp_syncookies = 1

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

$ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|;)' | grep -F net.ipv4.tcp_syncookies | tail -1

net.ipv4.tcp_syncookies = 1

If the network parameter "ipv4.tcp_syncookies" is not equal to "1" or nothing is returned, this is a finding.

Fix Text (F-61622r925857_fix)
Configure RHEL 9 to use TCP syncookies. Add or edit the following line in a system configuration file in the "/etc/sysctl.d/" directory: net.ipv4.tcp_syncookies = 1 Load settings from all system configuration files with the following command: $ sudo sysctl --system