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Description

Network security groups should be periodically evaluated for port misconfigurations. Where certain ports and protocols may be exposed to the Internet, they should be evaluated for necessity and restricted wherever they are not explicitly required.

Rationale​

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 sources for disrupting services of other machines on the Azure Virtual Network or even attack networked devices outside of Azure.

Audit​

This policy flagged an Azure Network Security Group as INCOMPLIANT if it contains at least one Inbound Security Rule that meets all of the following conditions:

  • Direction is Inbound.
  • Access is Allow.
  • Protocol is Udp.
  • Source Address Prefix is either Internet, * 0.0.0.0, /0, or Any.

If the Direction, Access, Protocol, or Source Address Prefix fields do not match the criteria above, the VM is marked as INAPPLICABLE.