Description:

Flow Logs is a feature that enables users to capture information about the IP traffic going to and from network interfaces in the organization's VPC Subnets. Once a flow log is created, the user can view and retrieve its data in Stackdriver Logging. It is recommended that Flow Logs be enabled for every business-critical VPC subnet.

Rationale:

VPC networks and subnetworks not reserved for internal HTTP(S) load balancing provide logically isolated and secure network partitions where GCP resources can be launched. When Flow Logs are enabled for a subnet, VMs within that subnet start reporting on all Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) flows.
Each VM samples the TCP and UDP flows it sees, inbound and outbound, whether the flow is to or from another VM, a host in the on-premises datacenter, a Google service, or a host on the Internet. If two GCP VMs are communicating, and both are in subnets that have VPC Flow Logs enabled, both VMs report the flows.

Flow Logs supports the following use cases:

Network monitoring
Understanding network usage and optimizing network traffic expenses
Network forensics
Real-time security analysis

Flow Logs provide visibility into network traffic for each VM inside the subnet and can be used to detect anomalous traffic or provide insight during security workflows.

The Flow Logs must be configured such that all network traffic is logged, the interval of logging is granular to provide detailed information on the connections, no logs are filtered, and metadata to facilitate investigations are included.

Note: Subnets reserved for use by internal HTTP(S) load balancers do not support VPC flow logs.

Standard pricing for Stackdriver Logging, BigQuery, or Cloud Pub/Sub applies. VPC Flow Logs generation will be charged starting in GA as described in reference: https://cloud.google.com/vpc/

ID	Name	CSP	Domain	Severity
AC_GCP_0032	Ensure Legacy Networks Do Not Exist for Older Projects	GCP	Infrastructure Security	LOW
AC_GCP_0031	Ensure private google access is enabled for Google Compute Subnetwork	GCP	Infrastructure Security	MEDIUM
AC_GCP_0033	Ensure that VPC Flow Logs is Enabled for Every Subnet in a VPC Network	GCP	Logging and Monitoring	MEDIUM

Detections

Analytics

Tenable Cloud Security Policies Search

LOW

MEDIUM

MEDIUM