The Ubuntu operating system must not be performing packet forwarding unless the system is a router.

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Associated with: CCI-000366

SV-90567r2_rule The Ubuntu operating system must not be performing packet forwarding unless the system is a router.

Vulnerability discussion

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this software is used when not required, system network information may be unnecessarily transmitted across the network.

Check content

Verify the Ubuntu operating system is not performing packet forwarding, unless the system is a router. Check to see if IP forwarding is enabled using the following command: # /sbin/sysctl -a | grep net.ipv4.ip_forward net.ipv4.ip_forward=0 If IP forwarding value is "1" and is not documented with the Information System Security Officer (ISSO) as an operational requirement , this is a finding.

Fix text

Configure the Ubuntu operating system to not allow packet forwarding, unless the system is a router with the following command: # sudo sysctl -w net.ipv4.ip_forward=0 If "0" 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.ip_forward=0

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