Title

Ubuntu OS must be configured to use TCP syncookies. (Cat II impact)

Discussion

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. 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 Ubuntu OS is configured to use TCP syncookies by using the following command: $ sysctl net.ipv4.tcp_syncookies net.ipv4.tcp_syncookies = 1 If the value is not "1", this is a finding. Check the saved value of TCP syncookies by using the following command: $ sudo grep -ir net.ipv4.tcp_syncookies /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /usr/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf /etc/sysctl.conf 2> /dev/null If the "net.ipv4.tcp_syncookies" option is not set to "1", is commented out, or is missing, this is a finding. If conflicting results are returned, this is a finding.

Fix Text

Configure Ubuntu OS to use TCP syncookies by using the following command: $ sudo sysctl -w net.ipv4.tcp_syncookies=1 If "1" is not the system's default value, add or update the following line in "/etc/sysctl.conf": net.ipv4.tcp_syncookies = 1

Additional Identifiers

Rule ID: SV-275616r1147898_rule

Vulnerability ID: V-275616

Group Title: SRG-OS-000142-GPOS-00071

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.