UDP services should be restricted from the Internet


Warning: This rule will be deprecated 18 December 2023 as part of the update to Azure CIS version 2.0.0


Disable internet exposed UDP ports on network security groups.


The potential security problem with broadly exposing UDP services over the internet is that attackers can use DDoS amplification techniques to reflect spoofed UDP traffic from Azure Virtual Machines. The most common types of these attacks use exposed DNS, NTP, SSDP, SNMP, CLDAP, and other UDP-based services as amplification source for disrupting services of other machines on the Azure Virtual Network or even attack networked devices outside of Azure.


Disable direct UDP access to your Azure Virtual Machines from the internet. After direct UDP access from the internet is disabled, you can use other options to access UDP-based services running on these virtual machines.


  1. https://docs.microsoft.com/en-us/azure/security/fundamentals/network-best-practices#secure-your-critical-azure-service-resources-to-only-your-virtual-networks
  2. https://docs.microsoft.com/en-us/azure/security/fundamentals/ddos-best-practices
  3. https://docs.microsoft.com/en-us/azure/security/benchmarks/security-controls-v2-network-security#ns-1-implement-security-for-internal-traffic

CIS Controls

Version 7

9.2 Ensure Only Approved Ports, Protocols and Services Are Running: Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.

7 Virtual Machines: This section covers security recommendations to follow to set virtual machine policies on an Azure subscription.