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

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Associated with: CCI-001095

SV-90549r2_rule The Ubuntu operating system must be configured to use TCP syncookies.

Vulnerability discussion

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. Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning.

Check content

Verify the Ubuntu operating system is configured to use TCP syncookies. Check the value of TCP syncookies with the following command: # sysctl net.ipv4.tcp_syncookies net.ipv4.tcp_syncookies = 1 If the value is not "1", this is a finding.

Fix text

Configure the Ubuntu operating system to use TCP syncookies, by running the following command: # sudo sysctl -w net.ipv4.tcp_syncookies=1 If "1" is not the system's default value then add or update the following line in "/etc/sysctl.conf" or in the appropriate file under "/etc/sysctl.d": net.ipv4.tcp_syncookies = 1

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