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The Photon operating system must be configured to use TCP syncookies.


Finding ID Version Rule ID IA Controls Severity
V-258829 PHTN-40-000068 SV-258829r933548_rule Medium
A TCP SYN flood attack can cause a Denial of Service (DOS) by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected and enables the system to continue servicing valid connection requests. Satisfies: SRG-OS-000142-GPOS-00071, SRG-OS-000420-GPOS-00186
VMware vSphere 8.0 vCenter Appliance Photon OS 4.0 Security Technical Implementation Guide 2023-10-29


Check Text ( C-62569r933546_chk )
At the command line, run the following command to verify TCP syncookies are enabled:

# /sbin/sysctl net.ipv4.tcp_syncookies

Example result:

net.ipv4.tcp_syncookies = 1

If "net.ipv4.tcp_syncookies" is not set to "1", this is a finding.
Fix Text (F-62478r933547_fix)
Navigate to and open:


Add or update the following line:

net.ipv4.tcp_syncookies = 1

At the command line, run the following command to load the new configuration:

# /sbin/sysctl --load /etc/sysctl.d/zz-stig-hardening.conf

Note: If the file zz-stig-hardening.conf does not exist, it must be created.