Check for Unrestricted RDP Access

Risk Level: Very High (act immediately)

Rule ID: Network-001

Ensure that Microsoft Azure network security groups (NSGs) do not allow unrestricted access (i.e. 0.0.0.0/0) on TCP port 3389 in order to protect against attackers that use brute force techniques to gain access to the Azure virtual machines associated with the NSGs. TCP port 3389 is used for secure remote GUI login to Microsoft VMs by connecting a Remote Desktop Protocol (RDP) client application with an RDP server.

This rule resolution is part of the Conformity Security & Compliance tool for Azure.

Security

Allowing unrestricted Remote Desktop Protocol (RDP) access can increase opportunities for malicious activities such as hacking, man-in-the-middle attacks (MITM) and Pass-the-Hash (PtH) attacks.

Audit

To determine if your Azure network security groups (NSGs) allow unrestricted access on TCP port 3389 (RDP), perform the following actions:

Using Azure Console

01 Sign in to Azure Management Console.

02 Navigate to All resources blade at https://portal.azure.com/#blade/HubsExtension/BrowseAll to access all your Microsoft Azure resources.

03 From the Subscription filter box, select the Azure account subscription that you want to examine.

04 From the Type filter box, select Network security group to list only the security groups available in the selected Azure subscription.

05 Click on the name of the network security group that you want to examine.

06 In the navigation panel, under Settings, select Inbound security rules to access the list with the inbound rules defined for the selected security group.

07 On the Inbound security rules page, verify the value available in the SOURCE column for any inbound/ingress rule with the PORT set to 3389 (RDP) and the PROTOCOL set to TCP. If one or more rules have the SOURCE set to Any (i.e. 0.0.0.0/0), the selected network security group allows unrestricted traffic on port 3389, thus the RDP access to the associated Microsoft Azure virtual machine(s) is not secured.

08 Repeat steps no. 5 – 7 for each network security group available in the current Azure subscription.

09 Repeat steps no. 3 – 8 for each subscription created in your Microsoft Azure cloud account.

Using Azure CLI

01 Run network nsg list command (Windows/macOS/Linux) using custom query filters to list the names of all network security groups (and the name of their associated resource groups) available in the current Azure subscription:

az network nsg list
	--output table
	--query '[*].{name:name, resourceGroup:resourceGroup}'

02 The command output should return a table with requested information:

Name                       ResourceGroup
------------------------   ------------------------------
cc-project5-server-nsg     cloud-shell-storage-westeurope
cc-production-server-nsg   cloud-shell-storage-westeurope

03 Run az network nsg rule list command (Windows/macOS/Linux) using the name of the Azure network security group that you want to examine and its associated resource group as identifier parameters to describe the RDP inbound rule defined for the selected network security group using custom query filtering:

az network nsg rule list
	--nsg-name cc-project5-server-nsg
	--resource-group cloud-shell-storage-westeurope
	--query "[?direction=='Inbound' && access=='Allow' && protocol=='TCP' && destinationPortRange=='3389']"

04 The command output should return the requested security group rule metadata or an empty array, i.e. [], if there is no RDP rule for TCP port 3389 defined:

[
  {
    "access": "Allow",
    "description": null,
    "destinationAddressPrefix": "*",
    "destinationAddressPrefixes": [],
    "destinationApplicationSecurityGroups": null,
    "destinationPortRange": "3389",
    "destinationPortRanges": [],
    "direction": "Inbound",
    "etag": "W/\"abcdabcd-abcd-abcd-abcd-abcdabcdabcd\"",
    "id": "/subscriptions/abcd1234-abcd-1234-abcd-1234abcd1234/resourceGroups/cloud-shell-storage-westeurope/providers/Microsoft.Network/networkSecurityGroups/cc-project5-server-nsg/securityRules/RDP",
    "name": "RDP",
    "priority": 300,
    "protocol": "TCP",
    "provisioningState": "Succeeded",
    "resourceGroup": "cloud-shell-storage-westeurope",
    "sourceAddressPrefix": "*",
    "sourceAddressPrefixes": [],
    "sourceApplicationSecurityGroups": null,
    "sourcePortRange": "*",
    "sourcePortRanges": [],
    "type": "Microsoft.Network/networkSecurityGroups/securityRules"
  }
]

If the "sourceAddressPrefix" attribute value is set to "*", "internet" or "any", as shown in the output example above, the selected network security group allows unrestricted traffic on TCP port 3389, therefore the Remote Desktop Protocol (RDP) access to any associated Microsoft Azure virtual machine(s) is not secured.

05 Repeat step no. 3 and 4 for each Azure network security group created in the selected subscription.

06 Repeat steps no. 1 – 5 for each subscription available within your Microsoft Azure cloud account.

Remediation / Resolution

To update your Azure NSG RDP rule configuration in order to restrict Remote Desktop Protocol access to specific entities such as IP addresses or IP ranges, perform the following actions:

Using Azure Console

01 Sign in to Azure Management Console.

02 Navigate to All resources blade at https://portal.azure.com/#blade/HubsExtension/BrowseAll to access all your Microsoft Azure resources.

03 From the Subscription filter box, select the Azure account subscription that you want to access.

04 From the Type filter box, select Network security group to list only the security groups available in the selected Azure subscription.

05 Click on the name of the network security group that you want to reconfigure.

06 In the navigation panel, under Settings, select Inbound security rules to access the list with the inbound rules defined for the selected security group.

07 On the Inbound security rules page, click on the noncompliant RDP security group rule that you want to reconfigure (see Audit section part I to identify the right rule).

08 On the selected security group rule configuration panel, perform the following:

Select IP Addresses from the Source dropdown list to allow inbound traffic on TCP port 3389 from specified IP addresses only.
For Source IP addresses/CIDR ranges, provide the source IP address, IP addresses or IP address ranges that will be allowed to access the virtual machines associated with the selected network security group. You can specify a single value or comma-separated list of multiple values. An example of multiple values is 192.168.1.10/32, 10.0.0.5/32.
Click Save to apply the changes.

09 Repeat steps no. 5 – 8 for each network security group that allows unrestricted inbound access on TCP port 3389 (RDP), available in the current Azure subscription.

10 Repeat steps no. 3 – 9 for each subscription created in your Microsoft Azure cloud account.

Using Azure CLI

01 Run network nsg rule update command (Windows/macOS/Linux) using the name of the network security group rule that you want to reconfigure as identifier parameter (see Audit section part II to identify the right NSG rule) to restrict RDP access to specific IP address(es) only by setting the --source-address-prefixes parameter to the IP address, IP addresses or IP address ranges that can be allowed to access the virtual machines associated with the selected network security group. You can specify a single value or a space-separated list of multiple values, as shown in the example below:

az network nsg rule update
	--name RDP
	--nsg-name cc-project5-server-nsg
	--resource-group cloud-shell-storage-westeurope
	--source-address-prefixes 192.168.99.1/32 192.168.1.10/32

02 The command output should return the metadata for the reconfigured Azure NSG rule:

{
  "access": "Allow",
  "description": null,
  "destinationAddressPrefix": "*",
  "destinationAddressPrefixes": [],
  "destinationApplicationSecurityGroups": null,
  "destinationPortRange": "3389",
  "destinationPortRanges": [],
  "direction": "Inbound",

  ...

  "name": "RDP",
  "priority": 300,
  "protocol": "TCP",
  "provisioningState": "Succeeded",
  "resourceGroup": "cloud-shell-storage-westeurope",
  "sourceAddressPrefix": "",
  "sourceAddressPrefixes": [
    "192.168.99.1/32",
    "192.168.1.10/32"
  ],
  "sourcePortRange": "*",
  "sourcePortRanges": [],
  "type": "Microsoft.Network/networkSecurityGroups/securityRules"
}

03 Repeat step no. 1 and 2 for each network security group that allows unrestricted inbound access on TCP port 3389 (RDP), available in the current Azure subscription.

04 Repeat steps no. 1 – 3 for each subscription created within your Microsoft Azure cloud account.

References

Azure Official Documentation
Azure network security overview
Network security groups
Create, change, or delete a network security group
Azure best practices for network security
CIS Microsoft Azure Foundations

Azure Command Line Interface (CLI) Documentation
az mysql server
az network nsg list
az network nsg rule list
az network nsg rule update

Publication date Apr 2, 2020

Audit

Using Azure Console

Using Azure CLI

Remediation / Resolution

Using Azure Console

Using Azure CLI

References

Related Network rules