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RDP access should not be accessible from the Internet, should be blocked on port 3389

Default Severity: critical

Explanation

RDP access can be configured on either the network security group or in the network security group rule.

RDP access should not be permitted from the internet (*, 0.0.0.0, /0, internet, any). Consider using the Azure Bastion Service.

Possible Impact

Anyone from the internet can potentially RDP onto an instance

Suggested Resolution

Block RDP port from internet

Insecure Example

The following example will fail the azure-network-disable-rdp-from-internet check. 

 resource "azurerm_network_security_rule" "bad_example" {
      name                        = "bad_example_security_rule"
      direction                   = "Inbound"
      access                      = "Allow"
      protocol                    = "TCP"
      source_port_range           = "*"
      destination_port_ranges     = ["3389"]
      source_address_prefix       = "*"
      destination_address_prefix  = "*"
 }

 resource "azurerm_network_security_group" "example" {
   name                = "tf-appsecuritygroup"
   location            = azurerm_resource_group.example.location
   resource_group_name = azurerm_resource_group.example.name

   security_rule {
     source_port_range           = "any"
      destination_port_ranges     = ["3389"]
      source_address_prefix       = "*"
      destination_address_prefix  = "*"
   }
 }

Secure Example

The following example will pass the azure-network-disable-rdp-from-internet check. 

 resource "azurerm_network_security_rule" "good_example" {
      name                        = "good_example_security_rule"
      direction                   = "Inbound"
      access                      = "Allow"
      protocol                    = "TCP"
      source_port_range           = "*"
      destination_port_ranges     = ["3389"]
      source_address_prefix       = "4.53.160.75"
      destination_address_prefix  = "*"
 }

 resource "azurerm_network_security_group" "example" {
   name                = "tf-appsecuritygroup"
   location            = azurerm_resource_group.example.location
   resource_group_name = azurerm_resource_group.example.name

   security_rule {
     source_port_range           = "any"
      destination_port_ranges     = ["3389"]
      source_address_prefix       = "4.53.160.75"
      destination_address_prefix  = "*"
   }
 }