So, you want to have a public IP Address for your application?

In Microsoft Azure, a public IP address is a fundamental component for enabling internet-facing services, such as hosting a web application, facilitating remote access, or exposing an API endpoint. While this connectivity drives functionality, it also exposes resources to the unpredictable and often hostile expanse of the internet. This blog dives deep into the security implications of a public IP in Azure, using a detailed scenario to illustrate potential threats and demonstrating how Azure’s robust toolkit—Network Security Groups (NSGs), Azure DDoS Protection, Azure Firewall, Web Application Firewall (WAF), Private Link, and Azure Bastion—can safeguard against them. 

Scenario: The exposed e-commerce platform 

Imagine a small e-commerce business launching its online store on Azure. The infrastructure includes an application gateway hosting a web server with a public IP (e.g., 20.55.123.45), an Azure SQL Database for inventory and customer data, and a load balancer distributing traffic. Initially, the setup works flawlessly, customers browse products, place orders, and the business grows. But one day, the IT team notices unusual activity: failed login attempts spike, site performance dips, and a customer reports a suspicious pop-up on the checkout page. The public IP left with minimal protection has become a target. 

The threats of public IP exposure 

A public IP is like an open address in a bustling digital city. It’s visible to anyone with the means to look, and without proper safeguards, it invites a variety of threats: 

Brute Force Attacks: Exposed endpoints, such as a VM with Remote Desktop Protocol (RDP) or SSH enabled, become prime targets for attackers attempting to guess credentials. With enough attempts, weak passwords can crumble, granting unauthorized access to sensitive systems. 

Exploitation of Vulnerabilities: Unpatched software or misconfigured services behind a public IP can be exploited. Attackers regularly scan for known vulnerabilities—like outdated web servers or databases—using automated tools to infiltrate systems and extract data or plant malware. 

Distributed Denial of Service (DDoS) Attacks: A public IP can attract floods of malicious traffic designed to overwhelm resources, rendering services unavailable. For businesses relying on uptime, this can lead to lost revenue and damaged trust. 

Application-Layer Attacks: Web applications exposed via a public IP are susceptible to threats like SQL injection, cross-site scripting (XSS), or other exploits that manipulate poorly secured code, potentially compromising data integrity or user privacy. 

Left unprotected, a public IP becomes a liability, amplifying the attack surface and inviting persistent threats from the internet’s darker corners. 

Azure’s Security Arsenal 

Azure provides a layered approach to securing resources with public IPs. By leveraging its built-in services, organizations can transform that open gateway into a fortified checkpoint. Here’s how these tools work together to mitigate risks: 
 

  
Azure DDoS Protection 
Azure DDoS Protection protects from overwhelming public IPs with malicious traffic. Azure DDoS Protection, available for infrastructure protection and as Network & IP Protection SKUs, monitors and mitigates these threats. The Network and IP Protection SKUs uses machine learning to profile normal traffic patterns, automatically detecting and scrubbing malicious floods—such as SYN floods or UDP amplification attacks—before they impact application availability. 

Azure Web Application Firewall (WAF) 
When a public IP fronts a web application (e.g., via Azure Application Gateway), the WAF adds application-layer protection. It inspects HTTP/HTTPS traffic, thwarting attacks like SQL injection or XSS by applying OWASP core rule sets. This is critical for workloads where the public IP serves as the entry point to customer-facing services. 

Network Security Groups (NSGs) 
NSGs act as a virtual firewall at the subnet or network interface level, filtering traffic based on predefined rules. For the specific scenario above, an NSG should be used to restrict inbound traffic to an Application Gateway’s public IP, allowing only specific ports (e.g., HTTPS on port 443) from trusted sources while blocking unsolicited RDP or SSH attempts. This reduces the attack surface by ensuring only necessary traffic reaches the resource. 

Azure Private Link 
Sometimes, the best defense is to avoid public exposure entirely. Azure Private Link allows resources—like Azure SQL Database or Storage—to be accessed over a private endpoint within a virtual network, bypassing the public internet. By pairing a public IP with Private Link for internal services, organizations can limit external exposure while maintaining secure, private connectivity. 

Azure Bastion 
For administrative access to backend VMs, exposing RDP or SSH ports via a public IP is a common risk. Azure Bastion eliminates this need by providing a fully managed, browser-based jump box. Admins connect securely through the Azure portal over TLS, reducing the chance of brute force attacks on open ports. 

Building a Secure Foundation 

A public IP in Azure doesn’t have to be a vulnerability, it can be a controlled entryway when paired with the right defenses. Start by applying the principle of least privilege with NSGs, restricting traffic to only what’s necessary. Layer on DDoS Protection and Azure Firewall for network-level resilience and add WAF for web-specific threats. Where possible, shift sensitive services to Private Link, and use Bastion for secure management. Together, these services create a multi-tiered shield, turning a potential weakness into a strength. 

In today’s threat landscape, a public IP is inevitable for many workloads. But leveraging Azure’s built in security tools, your organization can embrace the cloud’s connectivity while keeping threats at bay, allowing you to embrace the cloud without compromising security.