Detections
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3.9 Ensure VPC flow logging is enabled in all VPCs

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Information

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.

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:

https://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/SettingLogRetention.html

Solution

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

Sign into the management console

Select Services then VPC

In the left navigation pane, select Your VPCs

Select a VPC

In the right pane, select the Flow Logs tab.

If no Flow Log exists, click Create Flow Log

For Filter, select Reject

Enter in a Role and Destination Log Group

Click Create Log Flow

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.
From Command Line:

Create a policy document and name it as role_policy_document.json and paste the following content:

{
'Version': '2012-10-17',
'Statement': [
{
'Sid': 'test',
'Effect': 'Allow',
'Principal': {
'Service': 'ec2.amazonaws.com'
},
'Action': 'sts:AssumeRole'
}
]
}

Create another policy document and name it as iam_policy.json and paste the following content:

{
'Version': '2012-10-17',
'Statement': [
{
'Effect': 'Allow',
'Action':[
'logs:CreateLogGroup',
'logs:CreateLogStream',
'logs:DescribeLogGroups',
'logs:DescribeLogStreams',
'logs:PutLogEvents',
'logs:GetLogEvents',
'logs:FilterLogEvents'
],
'Resource': '*'
}
]
}

Run the below command to create an IAM role:

aws iam create-role --role-name <aws_support_iam_role> --assume-role-policy-document file://<file-path>role_policy_document.json

Run the below command to create an IAM policy:

aws iam create-policy --policy-name <ami-policy-name> --policy-document file://<file-path>iam-policy.json

Run attach-group-policy command using the IAM policy ARN returned at the previous step to attach the policy to the IAM role (if the command succeeds, no output is returned):

aws iam attach-group-policy --policy-arn arn:aws:iam::<aws-account-id>:policy/<iam-policy-name> --group-name <group-name>

Run describe-vpcs to get the VpcId available in the selected region:

aws ec2 describe-vpcs --region <region>

The command output should return the VPC Id available in the selected region.

Run create-flow-logs to create a flow log for the vpc:

aws ec2 create-flow-logs --resource-type VPC --resource-ids <vpc-id> --traffic-type REJECT --log-group-name <log-group-name> --deliver-logs-permission-arn <iam-role-arn>

Repeat step 8 for other vpcs available in the selected region.

Change the region by updating --region and repeat remediation procedure for other vpcs.

See Also

https://workbench.cisecurity.org/benchmarks/10599

Item Details

References: CCE|CCE-79202-8, CSCv7|6.2, CSCv7|12.5

Plugin: amazon_aws

Control ID: e71f7a21fbe116ddddbabf968132add933b009ba686ab047c3cd196ecf240b46