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

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

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.

Navigate to and open:

/etc/sysctl.d/zz-stig-hardening.conf

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.