STIGQter: STIG Summary: Cloud Linux AlmaLinux OS 9 Security Technical Implementation Guide Version: 1 Release: 7 Benchmark Date: 01 Jul 2026:

AlmaLinux OS 9 must be configured to use TCP syncookies.

DISA Rule

SV-269435r1050318_rule

Vulnerability Number

V-269435

Group Title

SRG-OS-000420-GPOS-00186

Rule Version

ALMA-09-042480

Severity

CAT II

CCI(s)

CCI-002385 - Protect against or limit the effects of organization-defined types of denial of service events.
CCI-001095 - Manage capacity, bandwidth, or other redundancy to limit the effects of information flooding types of denial of service attacks.

Weight

Fix Recommendation

Configure AlmaLinux OS 9 to use TCP syncookies using the following command:

$ echo 'net.ipv4.tcp_syncookies = 1' > /etc/sysctl.d/60-syncookies.conf

Load settings from all system configuration files with the following command:

$ sysctl --system

Check Contents

Verify AlmaLinux OS 9 is configured to use IPv4 TCP syncookies with the following command:

$ sysctl net.ipv4.tcp_syncookies

net.ipv4.tcp_syncookies = 1

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

$ /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.

Vulnerability Number

V-269435

Documentable

False

Rule Version

ALMA-09-042480

Severity Override Guidance

Check Content Reference

Target Key

5664