AWS creates default VPCs in each region for convenience. However, these default VPCs often contain noncompliant network ACLs and security group rules that do not align with best practices for AWS Config and Security Hub. Deleting these default VPCs is beneficial, especially for regions not used by your organization or architectures that do not utilize a VPC.
This guide demonstrates how to use StackQL to enumerate and delete all default VPCs and their associated resources in all AWS regions.
What you need
All you need to do is to install the pystackql package using:
pip install pystackql
Deleting resources will require a privileged AWS IAM user. You can do this from a terminal with the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables set (and optionally AWS_SESSION_TOKEN set if you are using sts assume-role).
You can also use the StackQL Cloud Shell Scripts, from within AWS Cloud Shell, to run authenticated StackQL queries using:
sh stackql-aws-cloud-shell.sh
How it works
Default VPCs in AWS regions have a CIDR block of 172.31.0.0/16, before deleting anything, the program ensures it is not in use by using:
SELECT
id
FROM aws.ec2.network_interfaces
WHERE region = '{region}'
AND vpc_id = '{vpc_id}'
If any resources are using the VPC (such as EC2, RDS, ELB/ALB, VPC attached Lambda functions, etc), it will skip these VPCs. Once determined that the VPC is not in use, all of the resources associated with the VPC must be deleted before the VPC itself can be deleted; this includes:
- External Routes (aws.ec2.routes)
- Internet Gateways (aws.ec2.internet_gateways)
- NACLs (aws.ec2.network_acls)
- Subnets (aws.ec2.subnets)
- and then finally, the VPC (aws.ec2.vpcs)
The default route table and default security group are deleted automatically when deleting the VPC
This is done by discovering the resources using StackQL SELECT queries and deleting them using StackQL DELETE queries, like:
DELETE FROM aws.ec2.network_acls
WHERE data__Identifier = '{nacl_id}'
AND region = '{region}'
Complete code
The following Python program uses StackQL to list and delete default VPCs and their associated resources (subnets, route tables, internet gateways, security groups, and network ACLs) across all AWS regions.
Get the complete code here
from pystackql import StackQL
stackql = StackQL()
stackql.executeStmt("REGISTRY PULL aws")
def ensure_one_or_zero(resource_list, resource_name, region):
if len(resource_list) > 1:
raise RuntimeError(f"ah snap! multiple default {resource_name} resources found in {region}")
elif len(resource_list) == 0:
print(f"/* no default {resource_name} found in {region} */\n")
return False
return True
regions = [
'us-east-1', 'us-east-2', 'us-west-1', 'us-west-2',
'eu-central-1', 'eu-central-2', 'eu-west-1', 'eu-west-2', 'eu-west-3', 'eu-north-1', 'eu-south-1',
'ap-east-1', 'ap-south-1', 'ap-south-2', 'ap-northeast-1', 'ap-northeast-2', 'ap-northeast-3',
'ap-southeast-1', 'ap-southeast-2', 'ap-southeast-3', 'ap-southeast-4', 'af-south-1',
'ca-central-1', 'me-south-1', 'me-central-1', 'sa-east-1'
]
for region in regions:
vpc_ids = stackql.execute(
f"""
SELECT
vpc_id
FROM aws.ec2.vpcs
WHERE region = '{region}'
AND cidr_block = '172.31.0.0/16'
AND JSON_ARRAY_LENGTH(tags) = 0
"""
)
if not ensure_one_or_zero(vpc_ids, 'VPC', region): continue
vpc_id = vpc_ids[0]['vpc_id']
# check if vpc is in use
network_interfaces = stackql.execute(
f"""
SELECT
id
FROM aws.ec2.network_interfaces
WHERE region = '{region}'
AND vpc_id = '{vpc_id}'
"""
)
if len(network_interfaces) > 0:
print(f"/* skipping deletion of default VPC ({vpc_id}) in {region} because it is in use */\n")
continue
print(f"/* deleting resources for default VPC ({vpc_id}) in {region} */\n")
# get route table
route_table_ids = stackql.execute(
f"""
SELECT
route_table_id
FROM aws.ec2.route_tables
WHERE region = '{region}'
AND vpc_id = '{vpc_id}'
"""
)
ensure_one_or_zero(route_table_ids, 'route table', region)
route_table_id = route_table_ids[0]['route_table_id']
# get inet gateway id
inet_gateway_ids = stackql.execute(
f"""
SELECT gateway_id
FROM aws.ec2.routes
WHERE data__Identifier = '{route_table_id}|0.0.0.0/0'
AND region = '{region}'
"""
)
ensure_one_or_zero(inet_gateway_ids, 'internet gateway', region)
inet_gateway_id = inet_gateway_ids[0]['gateway_id']
# delete routes
print(f"/* deleting default VPC routes in route table ({route_table_id}) in {region} */")
print(f"""
DELETE FROM aws.ec2.routes
WHERE data__Identifier = '{route_table_id}|0.0.0.0/0'
AND region = '{region}';
""")
# detatch inet gateway
print(f"/* detaching default VPC internet gateway ({inet_gateway_id}) in {region} */")
print(f"""
DELETE FROM aws.ec2.vpc_gateway_attachments
WHERE data__Identifier = 'IGW|{vpc_id}'
AND region = '{region}';
""")
# delete inet gateway
print(f"/* deleting default VPC internet gateway ({inet_gateway_id}) in {region} */")
print(f"""
DELETE FROM aws.ec2.internet_gateways
WHERE data__Identifier = '{inet_gateway_id}'
AND region = '{region}';
""")
# delete nacl
nacl_ids = stackql.execute(
f"""
SELECT
id
FROM aws.ec2.network_acls
WHERE vpc_id = '{vpc_id}'
AND region = '{region}'
"""
)
ensure_one_or_zero(nacl_ids, 'network acl', region)
nacl_id = nacl_ids[0]['id']
print(f"/* deleting default VPC NACL ({nacl_id}) in {region} */")
print(f"""
DELETE FROM aws.ec2.network_acls
WHERE data__Identifier = '{nacl_id}'
AND region = '{region}';
""")
# delete subnets
subnet_ids = stackql.execute(
f"""
SELECT
subnet_id
FROM aws.ec2.subnets
WHERE vpc_id = '{vpc_id}'
AND region = '{region}'
"""
)
for subnet_id in subnet_ids:
print(f"/* deleting default VPC subnet ({subnet_id['subnet_id']}) in {region} */")
print(f"""
DELETE FROM aws.ec2.subnets
WHERE data__Identifier = '{subnet_id['subnet_id']}'
AND region = '{region}';
""")
# delete vpc
print(f"/* deleting default VPC ({vpc_id}) in {region} */")
print(f"""
DELETE FROM aws.ec2.vpcs
WHERE data__Identifier = '{vpc_id}'
AND region = '{region}';
""")
run the program using:
python3 delete-all-default-vpcs.py > delete_default_vpcs.iql
to generate a StackQL script you can run as a batch using stackql exec or as individual statements in the stackql shell.
Conclusion
Deleting default VPCs can help improve your AWS security posture by removing potentially noncompliant network configurations. This program leverages StackQL to automate the process, ensuring consistency across all regions.
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