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 enable VPC Flow Logs:

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 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, name it 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, name it 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 following 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

4. Run the following command to create an IAM policy:

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

5. Run the attach-group-policy command, using the IAM policy ARN returned from the previous step to attach the policy to the IAM role:

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

If the command succeeds, no output is returned.

6. Run the describe-vpcs command to get a list of VPCs in the selected region:

aws ec2 describe-vpcs --region <region>

The command output should return a list of VPCs in the selected region.

7. Run the create-flow-logs command to create a flow log for a 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>

8. Repeat step 7 for other VPCs in the selected region.
9. Change the region by updating --region, and repeat the remediation procedure for each region.