---
title: Sensitive port is exposed to small public network
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > Code Security > Infrastructure as Code (IaC)
  Security > IaC Security Rules > Sensitive port is exposed to small public
  network
---

# Sensitive port is exposed to small public network

{% callout %}
# Important note for users on the following Datadog sites: app.ddog-gov.com, us2.ddog-gov.com

{% alert level="danger" %}
This product is not supported for your selected [Datadog site](https://docs.datadoghq.com/getting_started/site.md). ({% placeholder "user-datadog-site-name" /%}).
{% /alert %}

{% /callout %}

## Metadata{% #metadata %}

**Id:** `terraform-azure-sensitive-port-is-exposed-to-small-public-network` 

**Provider:** Azure

**Platform:** Terraform

**Severity:** Medium

**Category:** Networking and Firewall

#### Learn More{% #learn-more %}

- [Provider Reference](https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/network_security_rule)

### Description{% #description %}

Allowing sensitive ports, such as port 23 (Telnet) or port 110 (POP3), to be open on public-facing network security groups exposes your resources to potential attacks that target these outdated and insecure protocols. Attackers can exploit these open ports to gain unauthorized access, intercept unencrypted communications, or conduct brute-force attacks against your infrastructure. To mitigate this risk, network security rules should explicitly deny traffic on sensitive ports, as in the following secure configuration:

```
resource "azurerm_network_security_rule" "secure_example" {
     name                        = "deny_telnet"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Deny"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "*"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}
```

## Compliant Code Examples{% #compliant-code-examples %}

```terraform
resource "azurerm_network_security_rule" "negative1" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Deny"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "*"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative2" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "Icmp"
     source_port_range           = "*"
     destination_port_range      = "23-34"
     source_address_prefix       = "*"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative3" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "8-174"
     source_address_prefix       = "0.0.0.0"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative4" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23-196"
     source_address_prefix       = "192.168.0.0"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative5" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "/1"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative6" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "*"
     source_port_range           = "*"
     destination_port_range      = "43"
     source_address_prefix       = "/0"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative7" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "Icmp"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "internet"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative8" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "*"
     source_port_range           = "*"
     destination_port_range      = "22, 24,49-67"
     source_address_prefix       = "any"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative9" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "Icmp"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "/0"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative10" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23 ,  69"
     source_address_prefix       = "0.0.1.0"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "negative11" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "2,310"
     source_address_prefix       = "0.0.0.0"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}
```

## Non-Compliant Code Examples{% #non-compliant-code-examples %}

```terraform
resource "azurerm_network_security_rule" "positive1" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "UDP"
     source_port_range           = "*"
     destination_port_range      = "61621"
     source_address_prefix       = "/26"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive2" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23-34"
     source_address_prefix       = "1.1.1.1/25"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive3" {
     name                        = "example"
     priority                      = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "*"
     source_port_range           = "*"
     destination_port_range      = "21-23"
     source_address_prefix       = "/26"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive4" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "*"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "0.0.0.0/27"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive5" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "UDP"
     source_port_range           = "*"
     destination_port_range      = "23,245"
     source_address_prefix       = "34.15.11.3/28"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive6" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "23"
     source_address_prefix       = "/29"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive7" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "UDP"
     source_port_range           = "*"
     destination_port_range      = "22-64, 94"
     source_address_prefix       = "10.0.0.0/28"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive8" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "TCP"
     source_port_range           = "*"
     destination_port_range      = "14, 23, 48"
     source_address_prefix       = "12.12.12.12/27"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive9" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "*"
     source_port_range           = "*"
     destination_port_range      = "12, 23-24,46"
     source_address_prefix       = "/26"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}

resource "azurerm_network_security_rule" "positive10" {
     name                        = "example"
     priority                    = 100
     direction                   = "Inbound"
     access                      = "Allow"
     protocol                    = "*"
     source_port_range           = "*"
     destination_port_range      = "46-146, 18-36, 1-2, 3"
     source_address_prefix       = "1.2.3.4/25"
     destination_address_prefix  = "*"
     resource_group_name         = azurerm_resource_group.example.name
     network_security_group_name = azurerm_network_security_group.example.name
}
```