The system must be configured to use TCP syncookies when experiencing a TCP SYN flood.

From Red Hat Enterprise Linux 5 Security Technical Implementation Guide

Associated with IA controls: ECSC-1

Associated with: CCI-001092

SV-37633r1_rule The system must be configured to use TCP syncookies when experiencing a TCP SYN flood.

Vulnerability discussion

A TCP SYN flood attack can cause Denial of Service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies are a mechanism used to only track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This technique does not operate in a fully standards-compliant manner, but is only activated when a flood condition is detected, and allows defense of the system while continuing to service valid requests.

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Fix text

Configure the system to use TCP syncookies when experiencing a TCP SYN flood. Edit /etc/sysctl.conf and add a setting for "net.ipv4.tcp_syncookies=1". # sysctl -p

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