AWSOverview
A VPC comes with a default security group whose initial settings deny all inbound traffic, allow all outbound traffic, and allow all traffic between instances assigned to the security group. If you don't specify a security group when you launch an instance, the instance is automatically assigned to this default security group. Security groups provide stateful filtering of ingress/egress network traffic to AWS resources. It is recommended that the default security group restrict all traffic. The default VPC in every region should have its default security group updated to comply. Any newly created VPCs will automatically contain a default security group that will need remediation to comply with this recommendation.
NOTE When implementing this recommendation, VPC flow logging is invaluable in determining the least privilege port access required by systems to work properly because it can log all packet acceptances and rejections occurring under the current security groups. This dramatically reduces the primary barrier to least privilege engineering - discovering the minimum ports required by systems in the environment. Even if the VPC flow logging recommendation in this benchmark is not adopted as a permanent security measure, it should be used during any period of discovery and engineering for least privileged security groups.
Rationale
Configuring all VPC default security groups to restrict all traffic will encourage least privilege security group development and mindful placement of AWS resources into security groups which will in-turn reduce the exposure of those resources.
Remediation guidance
Security Group Members
Perform the following to implement the prescribed state:
- Identify AWS resources that exist within the default security group
- Create a set of least privilege security groups for those resources
- Place the resources in those security groups
- Remove the resources noted in #1 from the default security group
Security Group State
- Login to the AWS Management Console at https://console.aws.amazon.com/vpc/home
- Repeat the next steps for all VPCs - including the default VPC in each AWS region:
- In the left pane, click
Security Groups - For each default security group, perform the following:
- Select the
defaultsecurity group - Click the
Inbound Rulestab - Remove any inbound rules
- Click the
Outbound Rulestab - Remove any outbound rules
Recommended
IAM groups allow you to edit the "name" field. After remediating default groups rules for all VPCs in all regions, edit this field to add text similar to "DO NOT USE. DO NOT ADD RULES"
Impact
Implementing this recommendation in an existing VPC containing operating resources requires extremely careful migration planning as the default security groups are likely to be enabling many ports that are unknown. Enabling VPC flow logging (of accepts) in an existing environment that is known to be breach free will reveal the current pattern of ports being used for each instance to communicate successfully.
References
- CCE-79201-0
- https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-network-security.html
- https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-security-groups.html#default-security-group
Service-wide remediation
Recommended when many resources are affected: fix the platform baseline first so new resources inherit the secure setting, then remediate the existing flagged resources in batches.
AWS
Use AWS Organizations guardrails, AWS Config rules or conformance packs where they fit, approved account baselines, and IaC modules so new resources inherit the secure setting.
Operational rollout
- Fix the baseline first at the account, subscription, project, cluster, or tenant scope that owns this control.
- Remediate the currently affected resources in batches, starting with internet-exposed and production assets.
- Re-scan and track approved exceptions with an owner and expiry date.
Query logic
These are the stored checks tied to this control.
The default security group of every VPC restricts all traffic
Connectors
Covered asset types
Expected check: eq []
{
securityGroups(where: { groupName: "default", NOT: { rules_SOME: null } }) {
...AssetFragment
}
}
