Ensure that UDP Port Access from the Internet is Evaluated and Restricted

HighLevel 1Manual reviewazure

Description

Network security groups should be periodically evaluated for port misconfigurations. Where UDP is not explicitly required and narrowly configured for resources attached to a network security group, Internet-level access to Azure resources should be restricted or eliminated. 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 exploit exposed DNS, NTP, SSDP, SNMP, CLDAP, and other UDP-based services as amplification sources to disrupt services on other machines within the Azure Virtual Network, or even attack networked devices outside of Azure.

How it is checked

Audit method: Manual review

This recommendation cannot be checked automatically. A scan lists it with these instructions when you pass --include-manual.

Audit from Azure Portal 1. Go to Network security groups. 2. Click the name of a network security group. 3. Under Settings, click Inbound security rules. 4. Ensure that no inbound security rule exists that matches the following: o Port: 53, 123, 161, 389, or 1900, or range including 53, 123, 161, 389, or 1900. o Protocol: UDP or Any o Source: 0.0.0.0/0, Internet, or Any o Action: Allow 5. Repeat steps 1-4 for each network security group. To audit from Azure Resource Graph: 1. Go to Resource Graph Explorer. 2. Click New query. 3. Paste the following into the query window: resources | where type =~ "microsoft.network/networksecuritygroups" | project id, name, securityRule = properties.securityRules | mv-expand securityRule | extend access = securityRule.properties.access, direction = securityRule.properties.direction, protocol = securityRule.properties.protocol, destinationPort = case(isempty(securityRule.properties.destinationPortRange), securityRule.properties.destinationPortRanges, securityRule.properties.destinationPortRange), sourceAddress = case(isempty(securityRule.properties.sourceAddressPrefix), securityRule.properties.sourceAddressPrefixes, securityRule.properties.source...

How it is fixed

Fix method: Guidance or infrastructure patch

Remediate from Azure Portal 1. Go to Network security groups. 2. Click the name of a network security group. 3. Under Settings, click Inbound security rules. 4. Check the box next to any inbound security rule matching: o Port: Port: 53, 123, 161, 389, or 1900, or range including 53, 123, 161, 389, or 1900. o Protocol: UDP or Any o Source: 0.0.0.0/0, Internet, or Any o Action: Allow 5. Click Delete. 6. Click Yes. 7. Repeat steps 1-6 for each network security group requiring remediation. Remediate from Azure CLI For each network security group rule requiring remediation, run the following command to delete the rule: az network nsg rule delete --resource-group <resource-group> --nsg-name <network-security-group> --name <rule>

Properties

Operating systems: Any
Tags: access-controlazurecloud
Reference: CIS Microsoft Azure Foundations Benchmark v6.0.0 - 7.3 Ensure that UDP Port Access from the Internet is Evaluated and Restricted