Profile Applicability: Level 2


Description: 

VPC Flow Logs is a feature that enables you to capture information about the IP traffic going to and from network interfaces in your VPC. After you've created a flow log, you can view and retrieve its data in Amazon CloudWatch Logs. It is recommended that VPC Flow Logs be enabled for packet "Rejects" for VPCs. 


Rationale: 

VPC Flow Logs provide visibility into network traffic that traverses the VPC and can be used to detect anomalous traffic or insight during security workflows.


Audit: 

Perform the following to determine if VPC Flow logs is enabled: Via the Management Console: 

1. Sign into the management console 

2. Select Services then VPC 

3. In the left navigation pane, select Your VPCs 

4. Select a VPC 

5. In the right pane, select the Flow Logs tab. 

6. Ensure a Log Flow exists that has Active in the Status column.


Remediation:

Perform the following to determine if VPC Flow logs is enabled: Via the Management Console: 

1. Sign into the management console 

2. Select Services then VPC 

3. In the left navigation pane, select Your VPCs 

4. Select a VPC 

5. In the right pane, select the Flow Logs tab. 

6. If no Flow Log exists, click Create Flow Log 

7. For Filter, select Reject 

8. Enter in a Role and Destination Log Group 

9. Click Create Log Flow

10. Click on CloudWatch Logs Group

Note: Setting the filter to "Reject" will dramatically reduce the logging data accumulation for this recommendation and provide sufficient information for the purposes of breach detection, research and remediation. However, during periods of least privilege security group engineering, setting this the filter to "All" can be very helpful in discovering existing traffic flows required for proper operation of an already running environment.

Impact: 

By default, CloudWatch Logs will store Logs indefinitely unless a specific retention period is defined for the log group. When choosing the number of days to retain, keep in mind the average days it takes an organization to realize they have been breached is 210 days (at the time of this writing). Since additional time is required to research a breach, a minimum 365 day retention policy allows time for detection and research. You may also wish to archive the logs to a cheaper storage service rather than simply deleting them. See the following AWS resource to manage CloudWatch Logs retention periods:

    1. http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/SettingL ogRetention.html


Reference: 

1. CCE-79202-8 

2. CIS CSC v6.0 #6.5, #12.9 

3. http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/flow-logs.html 

Notes: Changed title from "Ensure VPC flow logging is enabled in all applicable regions" to "Ensure VPC flow logging is enabled in all VPCs" For these reasons: 

1. Flow logs cannot be enabled for regions, only for VPCs 

2. The statement did not define an "Applicable Region" and did not clarify "all VPCs in applicable regions" 

3. All other benchmark recommendations appear to assume that you apply them "any actively used configuration or resource" or "All resources" - so specifying "applicable" to mean "active" or "compliant with the benchmark" seems unnecessary


CIS Controls:

6.2 Activate audit logging 

    Ensure that local logging has been enabled on all systems and networking devices. 

12.5 Configure Monitoring Systems to Record Network Packets 

    Configure monitoring systems to record network packets passing through the boundary at each of the organization's network boundaries.