VPC security group rules should not permit ingress from ‘0.0.0.0/0’ to TCP/UDP port 139 (NetBios Session Service)

Description

VPC security group rules should not permit ingress from ‘0.0.0.0/0’ to TCP/UDP port 139 (NetBios Session Service). Removing unfettered connectivity to a NetBios Session Service server reduces the chance of exposing critical data.

Console Remediation Steps

  • Navigate to VPC.

  • In the left pane, click Security Groups.

  • For each security group, perform the following:

    • Select the security group.

    • Click the Inbound Rules tab.

    • Identify the rules to be removed.

    • Click the x in the Remove column.

    • Click Save.

CLI Remediation Steps for TCP

  • Remove the inbound rule(s) that permits unrestricted ingress to TCP port 139 from the selected Security Group:

    • aws ec2 revoke-security-group-ingress --region <region> --group-name <group_name> --protocol tcp --port 139 --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 tcp --port 139 --cidr <cidr_block>

CLI Remediation Steps for UDP

  • Remove the inbound rule(s) that permits unrestricted ingress to UDP port 139 from the selected Security Group:

    • aws ec2 revoke-security-group-ingress --region <region> --group-name <group_name> --protocol udp --port 139 --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 udp --port 139 --cidr <cidr_block>