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AlmaLinux OS 9 must be configured to use TCP syncookies.

Overview

Finding IDVersionRule IDIA ControlsSeverity
V-269435ALMA-09-042480SV-269435r1050318_ruleCCI-002385medium
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. This requirement addresses the configuration of the operating system to mitigate the impact of DoS attacks that have occurred or are ongoing on system availability. For each system, known and potential DoS attacks must be identified and solutions for each type implemented. A variety of technologies exist to limit or, in some cases, eliminate the effects of DoS attacks (e.g., limiting processes or establishing memory partitions). Employing increased capacity and bandwidth, combined with service redundancy, may reduce the susceptibility to some DoS attacks. Satisfies: SRG-OS-000420-GPOS-00186, SRG-OS-000142-GPOS-00071
STIGDate
Cloud Linux AlmaLinux OS 9 Security Technical Implementation Guide2026-02-27

Related Frameworks

1 mapping across 4 frameworks
SCF0 mappings

No source states a mapping between these directly.

Also reachable in 3 hops (13) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

MON-01Continuous Monitoring
1.00
MON-01.1Intrusion Detection & Prevention Systems (IDS & IPS)
1.00
MON-01.3Inbound & Outbound Communications Traffic
1.00
MON-01.4System Generated Alerts
1.00
MON-01.8Security Event Monitoring
1.00
NET-01Network Security Controls (NSC)
1.00
NET-02Layered Network Defenses
1.00
SEA-01Secure Engineering Principles
1.00
SEA-02Alignment With Enterprise Architecture
1.00
CAP-01Capacity & Performance Management
0.50

+3 more (top 10 by confidence shown)

NIST 800-530 mappings

No source states a mapping between these directly.

Also reachable in 2 hops (36) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

AC-10Concurrent Session Control
1.00
AC-17(9)Disconnect or Disable Access
1.00
AC-2(4)Automated Audit Actions
1.00
AC-3Access Enforcement
1.00
AC-4Information Flow Enforcement
1.00
AC-6(9)Log Use of Privileged Functions
1.00
AU-12Audit Record Generation
1.00
AU-3Content of Audit Records
1.00
AU-5Response to Audit Logging Process Failures
1.00
CM-11(2)Software Installation with Privileged Status
1.00

+26 more (top 10 by confidence shown)

CCI1 mapping
CCI-002385
1.00
NIST CSF 2.00 mappings

No source states a mapping between these directly.

Also reachable in 3 hops (3) derived by us, not asserted by any source

Each of these is a route we composed by chaining published mappings. No publisher states a relationship between the two endpoints.

DE.CM-01
1.00
PR.IR-01
1.00
PR.IR-04
0.50

Who does this work

12 NICE work roles and 9 EC-Council certifications.

This is an inference across published mappings, not a single claim by anyone. This check maps to a control, which maps to a Cybersecurity Framework outcome, which NIST assigns to the work roles below. EC-Council separately maps its certifications to those same roles.

A certification prepares someone for a role. It is not evidence that a holder is qualified, and neither NIST nor EC-Council has stated that any certification here addresses this check.

Work-role assignments published by NIST (NICE Framework Components 2.2.0 and the CSF 2.0 OLIR crosswalk). Certification mappings published by EC-Council.

Details

Check Text (C-269435r1050318_chk)

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.

Fix Text (F-73367r1049707_fix)

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