Control: 3.7 Ensure VPC flow logging is enabled in all VPCs

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.

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.

Remediation

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

From 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.

From Command Line:

1. 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"
}
]
}

2. 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": "*"
    }
  ]
}

3. Run the below command to create an IAM role:

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

4. 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

5. 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-accountid>:policy/<iam-policy-name> --group-name <group-name>

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

aws ec2 describe-vpcs --region <region>

7. The command output should return the VPC Id available in the selected region.
8. 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-logspermission-arn <iam-role-arn>

9. Repeat step 8 for other vpcs available in the selected region.
10. Change the region by updating --region and repeat remediation procedure for other vpcs.