VPC security group rules should not permit ingress from ‘0.0.0.0/0’ to TCP/UDP port 137 (NetBIOS Name Service)¶
Description¶
VPC security group rules should not permit ingress from ‘0.0.0.0/0’ to TCP/UDP port 137 (NetBIOS Name Service). Removing unfettered connectivity to a NetBIOS Name Service server reduces the chance of exposing critical data.
Remediation Steps¶
AWS Console¶
Navigate to VPC.
In the left navigation pane, click Security Groups.
Remove any rules that include port 137 and have a source of 0.0.0.0/0.
Click Save.
AWS CLI¶
List all security groups with an ingress rule of 0.0.0.0/0:
aws ec2 describe-security-groups --filters Name=ip-permission.cidr,Values='0.0.0.0/0' --query "SecurityGroups[*].{Name:GroupName,ID:GroupId}"
Remove the inbound rule(s) that permits unrestricted ingress to port 137:
aws ec2 revoke-security-group-ingress --region <region> --group-name <group_name> --protocol <protocol> --port 137 --cidr 0.0.0.0/0
Optionally add a more restrictive ingress rule to the selected Security Group:
aws ec2 authorize-security-group-ingress --region <region> --group-name <group_name> --protocol <protocol> --port 137 --cidr <cidr_block>
Terraform¶
Ensure that an aws_security_group
ingress
block does NOT contain both of the following:A
0.0.0.0/0
in thecidr_blocks
field137
is within the port range defined fromfrom_port
toto_port
, ORfrom_port
andto_port
are both set to0
Example Configuration¶
resource "aws_security_group" "example" {
ingress {
cidr_blocks = [10.0.0.0/16]
from_port = 137
to_port = 137
# other required fields here
}
}