Designing Outbound Connectivity for "Private Subnets" in Azure
Why Private Subnets Change Everything Historically, Azure virtual machines relied on default outbound internet access, where the platform automatically assigned a dynamic SNAT IP from a shared pool. This was convenient but problematic: ❌ No deterministic outbound IP addresses ❌ No traffic inspection or filtering ❌ No FQDN or URL governance ❌ Difficult to audit for compliance ❌ Susceptible to noisy neighbor SNAT exhaustion With private subnets, outbound access is disabled by default. This shifts the responsibility to the architect — deliberately. The result is an environment where: ✅ Every outbound flow is intentional ✅ Every outbound IP is known and documented ✅ Every egress path can be governed and logged ✅ Compliance evidence is straightforward to produce The question is no longer "does my VM have internet access?" but rather "how exactly does my VM reach the internet, and is that path appropriate for this workload?" The Three Outbound Patterns at a Glance Option Primary Role Inspection Scale Cost Best For NAT Gateway Managed outbound SNAT ❌ None ⭐⭐⭐ High 💲 Low Simple, scalable egress Azure Firewall Secure governed egress ✅ Full L3–L7 ⭐⭐⭐ High 💲💲💲 Higher Security boundaries Load Balancer Legacy SNAT ❌ None ⭐⭐ Limited 💲 Low Legacy / transitional Scenario 1: NAT Gateway What is NAT Gateway? Azure NAT Gateway is a fully managed, zone‑resilient, outbound‑only SNAT service. It attaches at the subnet level and automatically handles all outbound flows from that subnet using one or more static public IP addresses or prefixes. It is purpose‑built for one thing: providing predictable, scalable outbound internet access — without routing complexity or inline devices. Key flow are depicted below: VM → NAT Gateway: Automatic SNAT (no UDR required) NAT Gateway → Internet: Static, deterministic public IP Inbound: NOT supported (outbound only) How it works (step by step) VM initiates an outbound connection (e.g., HTTPS to an API) NAT Gateway intercepts the flow at the subnet boundary Source IP is translated to the NAT Gateway's static public IP The packet is forwarded to the internet Return traffic is automatically tracked and delivered back to the VM No UDRs. No routing tables. No inline devices. It just works. Strengths Massive SNAT scale — no port exhaustion concerns at typical enterprise scale Deterministic outbound IPs — easy to allowlist with external services Zone resilient — survives availability zone failures Subnet scoped — applies to all VMs in the subnet automatically No routing configuration required Limitations ❌ No traffic inspection or filtering ❌ No FQDN or URL policy enforcement ❌ No threat intelligence integration ❌ Cannot restrict which internet destinations are allowed Best Fit Use Cases ✅ Application tiers calling external SaaS APIs ✅ VMs requiring OS updates and patch downloads ✅ CI/CD build agents and pipeline runners ✅ Spoke VNets in hub‑and‑spoke where east‑west goes through firewall, but simple internet egress is acceptable ✅ Dev/test environments Scenario 2: Azure Firewall What is Azure Firewall? Azure Firewall is a cloud‑native, stateful, L3–L7 network security service. When used for outbound egress, it transforms the egress path from a connectivity function into a security enforcement boundary. Unlike NAT Gateway, Azure Firewall inspects every packet, evaluates it against policy, and either allows or denies it based on network rules, application rules, and threat intelligence feeds. KEY Flow are depicted below: VM → UDR: Forces ALL outbound traffic to Firewall Firewall: Evaluates against policy before allowing Firewall → Internet: Only explicitly permitted flows pass All denied flows: Logged and alertable How it works (step by step) VM initiates an outbound connection UDR intercepts the flow and redirects to Azure Firewall's private IP Azure Firewall evaluates the traffic: Network rules (IP/port match) Application rules (FQDN/URL match) Threat intelligence (known malicious IPs/domains) If allowed: traffic is forwarded via Firewall's public IP If denied: traffic is dropped and logged All flows (allowed and denied) are logged to Log Analytics / Sentinel Strengths ✅ Full L3–L7 inspection ✅ FQDN and URL‑based filtering (application rules) ✅ Threat intelligence integration (Microsoft TI feed) ✅ TLS inspection (Premium SKU) ✅ Centralized governance across multiple VNets via Firewall Manager ✅ Rich logging — every allowed and denied flow is recorded ✅ IDPS (Intrusion Detection and Prevention) available in Premium Limitations ❌ Higher cost (hourly + data processing charges) ❌ Requires UDR configuration on each spoke subnet ❌ Adds latency (small but non‑zero) ❌ Requires careful SNAT configuration at scale Best Fit Use Cases ✅ Regulated industries (financial services, healthcare, government) ✅ Any workload where outbound internet is a security boundary ✅ Environments requiring egress allowlisting for compliance ✅ Hub‑and‑spoke architectures with centralized control plane ✅ SOC environments needing outbound flow telemetry Scenario 3: Load Balancer Outbound What is Load Balancer Outbound? Azure Load Balancer outbound rules were historically the primary mechanism for providing SNAT to VMs behind a Standard Load Balancer. While newer patterns (NAT Gateway, Azure Firewall) have largely replaced this approach for new designs, outbound rules remain valid in specific scenarios. Key flows are depicted below: VMs → Load Balancer: Backend pool members get SNAT LB Outbound Rules: Define port allocation per VM ⚠️ Port exhaustion risk at scale ⚠️ No inspection or policy enforcement How it works (step by step) VM in the backend pool initiates an outbound connection Load Balancer applies SNAT using the frontend public IP Ephemeral ports are allocated per VM from a fixed pool Return traffic is tracked and delivered back to the correct VM If port pool is exhausted: connections fail (SNAT exhaustion) Strengths Lower cost than NAT Gateway or Firewall Tightly integrated with existing load‑balanced workloads Familiar operational model for legacy teams Limitations ❌ SNAT port pool is fixed and must be manually managed ❌ Risk of SNAT exhaustion at scale ❌ No traffic inspection ❌ Less flexible than NAT Gateway ❌ Not recommended for new designs Best Fit Use Cases ✅ Existing architectures already built around Azure Load Balancer ✅ Low outbound connection volume workloads ✅ Transitional architectures during modernization to NAT Gateway Decision Framework: Choosing the Right Outbound Pattern Common Pitfalls to Avoid ⚠️ Pitfall 1: Forgetting SNAT scale limits Load Balancer outbound rules allocate a fixed number of ephemeral ports per VM. At scale this exhausts quickly. Use NAT Gateway instead. ⚠️ Pitfall 2: Over‑securing low‑risk workloads Not every workload needs Azure Firewall for outbound. Dev/test and patch traffic are better served by NAT Gateway — simpler, cheaper, faster. ⚠️ Pitfall 3: Mixing outbound models in the same subnet NAT Gateway and Load Balancer outbound rules cannot coexist on the same subnet. NAT Gateway always takes precedence. Plan your subnet boundaries carefully. ⚠️ Pitfall 4: Blocking Azure platform dependencies Many Azure services still use public endpoints (even when Private Link is available). Ensure your outbound policy allows required Azure service tags before enforcing egress controls. ⚠️ Pitfall 5: Relying on platform defaults Default outbound access is retired for new VNets. Do not assume VMs can reach the internet without explicit configuration. Summary and Key Takeaways Scenario Best Choice Why Simple internet egress at scale NAT Gateway Scalable, predictable, no complexity Security boundary for egress Azure Firewall Inspection, FQDN rules, threat intel Legacy load‑balanced workloads Load Balancer Outbound Transitional only Regulated / compliance environments Azure Firewall Audit logs, policy enforcement Dev / test / patch traffic NAT Gateway Low cost, low friction The core principle Private subnets make outbound access intentional. Choose the outbound pattern that matches the risk level of the workload — not the most complex option available. References https://learn.microsoft.com/azure/nat-gateway/nat-overview https://learn.microsoft.com/azure/firewall/overview https://learn.microsoft.com/azure/load-balancer/outbound-rules https://azure.microsoft.com/blog/default-outbound-access-for-vms-in-azure-will-be-retired
Orchestrating Intrusion Detection and Prevention Signature overrides in Azure Firewall Premium
Introduction: Azure Firewall Premium provides strong protection with a built-in Intrusion Detection and Prevention System (IDPS). It inspects inbound, outbound, and east-west traffic against Microsoft’s continuously updated signature set and can block threats before they reach your workloads. IDPS works out of the box without manual intervention. However, in many environments administrators need the flexibility to override specific signatures to better align with operational or security requirements. Common reasons include: Compliance enforcement – enforcing policies that require certain threats (such as High severity signatures) to always be blocked, directional tuning or protocol/category-based tuning. Incident response – reacting quickly to emerging vulnerabilities by enabling blocking for newly relevant signatures. Noise reduction – keeping informational signatures in alert mode to avoid false positives while still maintaining visibility. In many environments, signature overrides are typically managed in one of two ways: Using the global IDPS mode Using the Azure portal to apply per-signature overrides individually While these approaches work, managing overrides manually becomes difficult when thousands of signatures are involved. The Azure portal also limits the number of changes that can be applied at once, which makes large tuning operations time-consuming. To simplify this process, this blog introduces an automation approach that allows you to export, filter, and apply IDPS signature overrides in bulk using PowerShell scripts. A Common Operational Scenario: Consider the following scenario frequently encountered by security teams: Scenario A security team wants to move their firewall from Alert → Alert + Deny globally to strengthen threat prevention. However, they do not want Low severity signatures to Deny traffic, because these signatures are primarily informational and may create unnecessary noise or false positives. Example: Signature ID: 2014906 Severity: Low Description: INFO – .exe File requested over FTP This signature is classified as informational because requesting an .exe file over FTP indicates contextual risk, not necessarily confirmed malicious activity. If the global mode is switched to Alert + Deny, this signature may start blocking traffic unnecessarily. The goal therefore becomes: Enable Alert + Deny globally Keep Low severity signatures in Alert mode The workflow described in this blog demonstrates how to achieve this outcome using the IDPS Override script. Automation Workflow: The automation process uses two scripts to export and update signatures. Workflow overview Azure Firewall Policy │ ▼ Export Signatures (ipssigs.ps1) │ ▼ CSV Review / Edit │ ▼ Bulk Update (ipssigupdate.ps1) │ ▼ Updated Firewall Policy Before implementing the workflow, it’s helpful to review the available IDPS modes and severity as seen below, very briefly. IDPS Modes: Severity: Prerequisites: Now that we understand Azure Firewall IDPS concepts and have the context for this script, let's get started with the workings of the script itself. First of all, let us ensure that you are connected to your Azure account and have selected the correct subscription. You can do so by running the following command: Connect-AzAccount -Subscription "<your-subscription-id>" Ensure the following modules are installed which are required for this operation: Az.Accounts Az.Network 💡 Tip: You can check if the above modules are installed by running the following command: Get-Module -ListAvailable Az* or check specific modules using this following commands: Get-module Az.Network | select Name, Version, Path Get-module Az.Accounts | select Name, Version, Path If you need to install/import them, run the following command which downloads all generally available Azure service modules from the PowerShell Gallery, overwriting existing versions without prompting: Import-Module Az.Network Import-Module Az.Accounts Restart PowerShell after installation. Configure ipsconfig.json Now, let's configure the ipsconfig.json file and ensure the configuration file contains your target environment details i.e., target subscription, target firewall policy resource group name, firewall name, firewall policy name, location and rule collection group name. Example: { "subs": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx", "rg": "TEST-RG", "fw": "fw", "fwp": "fw-policy", "location": "CentralUS", "rcg": "DefaultNetworkRuleCollectionGroup" } Note: Your account must have permissions to read and update firewall policy and IDPS settings. Running the Script: 1. Export Signatures Now that we have all the prerequisites ready, it's time to run the script. Run the following command in PS in the directory where the script exists: .\ipssigs.ps1 Now, the script should prompt for filtering criteria as shown below and you can input the values as per your requirements: For the example scenario that we considered, we will give the following inputs as shown above in the snapshot: Mode: Alert Severity: Low 💡 Tip: When specifying multiple values, ensure there is space between the 2 values but no comma, otherwise the script may return no results. The script now exports the results to ipssignatures_results.csv file by default (or a custom filename if specified). The exported CSV includes metadata such as severity, direction, group, and protocol, which can help inform tuning decisions. 2. Prepare the CSV Now, we do not need all of these columns when inputting the CSV file to update the Firewall Policy. We only need the following columns. Signature Id Mode Therefore, we will need to remove all other columns while keeping the SignatureId and mode columns along with their headers as seen below: 3. Update the Firewall Policy Now, it's time to update the Firewall Policy with the signature/mode overrides that we need using the above CSV file. However, please note that the script supports two operations: Changing the global IDPS mode Applying bulk signature overrides using the CSV file You can use either option independently or both together. Let's understand this further by looking at these 2 examples. Example 1: Change Global Mode and Override Low Severity Signatures Goal: Set global mode to Alert + Deny Keep Low severity signatures in Alert Command: .\ipssigupdate.ps1 -GlobalMode Deny -InputFile Lowseveritysignatures.csv Result: High and Medium signatures → Alert + Deny Low signatures → Alert Example 2: Override Signatures Only If the global mode should remain unchanged, then run the following command only. .\ipssigupdate.ps1 The script will then prompt for the input CSV file in the next step as seen below: As seen the changed were made to the Azure Firewall in just a few seconds. After the script completes, updated signature actions should appear in the firewall policy. 4. Monitoring Script Execution Please use the following commands to track and monitor the background processes, to verify the status, check for any error and remove completed jobs as seen below: You can check background job status using: Get-Job -Id <#> View results: Receive-Job -Id <#> -Keep Remove completed jobs: Remove-Job -Id <#> Note: Up to 10,000 IDPS rules can be customized at a time 5. Validate the Changes: Now that we finished running the script, it's time to verify the update by confirming: Global IDPS mode in the firewall policy Signature override state Alert or block events in your logging destination (Log Analytics or Microsoft Sentinel) Note: Please note that, while most signatures support Off, Alert, or Deny actions, there are some context-setting signatures, that have fixed actions and cannot be overridden. Conclusion: Azure Firewall Premium makes it straightforward to apply broad IDPS configuration changes through the Azure portal. However, as environments scale, administrators often require more precise and repeatable ways to manage signature tuning. The automation approach described in this blog allows administrators to query, review, and update thousands of signatures in minutes. This enables repeatable tuning workflows, improves operational efficiency, and simplifies large-scale security configuration changes. References: Github Repository for the IDPS scripts Azure Firewall IDPS Azure Firewall IDPS signature rule categories
Detect, correlate, contain: New Azure Firewall IDPS detections in Microsoft Sentinel and XDR
As threat actors continue to blend reconnaissance, exploitation, and post-compromise activity, network-level signals remain critical for early detection and correlated response. To strengthen this layer, we're introducing five new Azure Firewall IDPS detections, now available out of the box in the Azure Firewall solution for Microsoft Sentinel and Microsoft Defender XDR. See It in Action This short demo walks through Azure Firewall's IDPS capabilities, the new Sentinel detections, and the automated response playbook — from malicious traffic hitting the firewall to the threat being contained without manual intervention. Watch the demo → Azure Firewall integration with Microsoft Sentinel and Defender XDR Read on for the full details on each detection, customization options, and a step-by-step walkthrough of the automated response workflow. What’s new The Azure Firewall solution now includes five new analytic detections built on Azure Firewall. Detection name What it detects (network signal) MITRE ATT&CK tactic(s) Example ATT&CK techniques (representative) SOC impact High severity malicious activity Repeated high confidence IDPS hits such as exploit kits, malware C2, credential theft, trojans, shellcode delivery Initial access (TA0001) execution (TA0002) Command and Control (TA0011) Exploit public facing application (T1190) command and control over web protocols (T1071.001) Ingress Tool Transfer (T1105) Highlights active exploitation or post compromise behavior at the network layer; strong pivot point into XDR investigations Elevation of privilege attempt Repeated attempts or success gaining user or administrator privileges Privilege escalation (TA0004) Exploitation for privilege escalation (T1068) Flags critical inflection points where attackers move from foothold to higher impact control Web application attack Probing or exploitation attempts against web applications Initial access (TA0001) Exploit public facing application (T1190) Surfaces external attack pressure against internet facing apps protected by Azure Firewall Medium severity malicious activity Potentially unwanted programs, crypto mining, social engineering indicators, suspicious filenames/system calls Initial access (TA0001) execution (TA0002) impact (TA0040) User Execution (T1204) Resource Hijacking (T1496) Early stage or lower confidence signals that help teams hunt, monitor, and tune response before escalation Denial of Service (DoS) attack Attempted or sustained denial of service traffic patterns Impact (TA0040) Network Denial of Service (T1498) Enables faster DoS identification and escalation, reducing time to mitigation Where these detections apply These detections are available through the Azure Firewall solution in: Microsoft Sentinel, enabling SOC centric investigation, hunting, and automation Microsoft Defender XDR, allowing network level signals to participate in end-to-end attack correlation across identity, endpoint, cloud, and email They are powered by the AZFWIdpsSignature log table and require Azure Firewall with IDPS enabled (preferably with TLS inspection). Customizing the detections to fit your environment The Azure Firewall IDPS detections included in the Microsoft Sentinel solution are designed to be fully adaptable to customer environments, allowing SOC teams to tune sensitivity, scope, and signal fidelity based on their risk tolerance and operational maturity. Each detection is built on the AZFWIdpsSignature log table and exposes several clearly defined parameters that customers can modify without rewriting the analytic logic. 1. Tune alert sensitivity and time horizon Customers can adjust the lookback period (TimeWindow) and minimum hit count (HitThreshold) to control how aggressively the detection triggers. Shorter windows and lower thresholds surface faster alerts for high-risk environments, while longer windows and higher thresholds help reduce noise in high volume networks. 2. Align severity with internal risk models Each analytic rule includes a configurable minimum severity (MinSeverity) aligned to Azure Firewall IDPS severity scoring. Organizations can raise or lower this value to match internal incident classification standards and escalation policies. 3. Focus on relevant threat categories and behaviors Optional filters allow detections to be scoped to specific threat categories, descriptions, or enforcement actions. Customers can enable or disable: Category filtering to focus on specific attack classes (for example, command and control, exploit kits, denial of service, or privilege escalation). Description filtering to target specific behavioral patterns. Action filtering to alert only on denied or alerted traffic versus purely observed activity. This flexibility makes it easy to tailor detections for different deployment scenarios such as internet facing workloads, internal east-west traffic monitoring, or regulated environments with stricter alerting requirements. 4. Preserve structure while customizing output Even with customization, the detections retain consistent enrichment fields including source IP, threat category, hit count, severity, actions taken, and signature IDs ensuring alerts remain actionable and easy to correlate across Microsoft Sentinel and Microsoft Defender XDR workflows. By allowing customers to tune thresholds, scope, and focus areas while preserving analytic intent, these Azure Firewall IDPS detections provide a strong out of the box baseline that can evolve alongside an organization’s threat landscape and SOC maturity. Automated detection and response for Azure Firewall using Microsoft Sentinel In this walkthrough, we’ll follow a real-world attack simulation and see how Azure Firewall, Microsoft Sentinel, and an automated playbook work together to detect, respond to, and contain malicious activity, without manual intervention. Step 1: Malicious traffic originates from a compromised source A source IP address 10.0.100.20, hosted within a virtual network, attempts to reach a web application protected by Azure Firewall. To validate the scenario, we intentionally generate malicious outbound traffic from this source, such as payloads that match known attack patterns. This is an outbound flow, meaning the traffic is leaving the internal network and attempting to reach an external destination through Azure Firewall. At this stage: Azure Firewall is acting as the central enforcement point Traffic is still allowed, but deep packet inspection is in effect Step 2: Azure Firewall IDPS detects malicious behavior Azure Firewall's intrusion detection and prevention system (IDPS) is enabled and inspects traffic as it passes through the firewall. When IDPS detects patterns that match known malicious signatures, the action taken depends on the signature's configured mode: Alert mode: IDPS generates a detailed security log for the matched signature but allows the traffic to continue. This is useful for monitoring and tuning before enforcing blocks. Alert and Deny mode: IDPS blocks the matching traffic and generates a detailed security log. The threat is stopped at the network layer while full telemetry is preserved for investigation. In both cases, IDPS records rich metadata including source IP, destination, protocol, signature name, severity, and threat category. These logs are what power the downstream detections in Microsoft Sentinel. In this walkthrough, the signature is configured in Alert and Deny mode, meaning the malicious traffic from 10.0.100.20 is blocked immediately at the firewall while the corresponding log is forwarded for analysis. Step 3: Firewall logs are sent to Log Analytics All Azure Firewall logs, including IDPS logs, are sent to a Log Analytics workspace named law-cxeinstance. At this point: Firewall logs are centralized Logs are normalized and can be queried No alerting has happened yet, only data collection This workspace becomes the single source of truth for downstream analytics and detections. Step 4: Microsoft Sentinel ingests and analyzes the Firewall logs The Log Analytics workspace is connected to Microsoft Sentinel, which continuously analyzes incoming data. Using the Azure Firewall solution from the Sentinel Content Hub, we previously deployed a set of built-in analytic rule templates designed specifically for Firewall telemetry. One of these rules is: “High severity malicious activity detected”. This rule evaluates IDPS logs and looks for: High-confidence signatures, known exploit techniques and malicious categories identified by Firewall IDPS. Step 5: Sentinel creates an incident When the analytic rules are met, Microsoft Sentinel automatically: Raises an alert Groups related alerts into an incident Extracts entities such as IP addresses, severity, and evidence In this case, the source IP 10.0.100.20 is clearly identified as the malicious actor and attached as an IP entity to the incident. This marks the transition from detection to response. Step 6: An automation rule triggers the playbook To avoid manual response, we configured a Sentinel automation rule that triggers whenever: An incident is created The analytic rule name matches any of the analytic rules we configured The automation rule immediately triggers a Logic App playbook named AzureFirewallBlockIPaddToIPGroup. This playbook is available as part of the Azure Firewall solution and can be deployed directly from the solution package. In addition, a simplified version of the playbook is published in our GitHub repository, allowing you to deploy it directly to your resource group using the provided ARM template. This is where automated containment begins. Step 7: The playbook aggregates and updates the IP Group The playbook performs several critical actions in sequence: Extracts IP entities from the Sentinel incident Retrieves the existing Azure Firewall IP Group named MaliciousIPs Checks for duplicates to avoid unnecessary updates Aggregates new IPs into a single array/list Updates the IP Group in a single operation. It is important to note that the playbook managed identity should have contributor access on the IP Group or its resource group to perform this action. In our scenario, the IP 10.0.100.20 is added to the MaliciousIPs IP Group. Step 8: Firewall policy enforces the block immediately Azure Firewall already has a network rule named BlockMaliciousTraffic configured with: Source: MaliciousIPs IP Group Destination: Any Protocol: Any Action: Deny Because the rule references the IP Group dynamically, the moment the playbook updates MaliciousIPs, the firewall enforcement takes effect instantly — without modifying the rule itself. Traffic originating from 10.0.100.20 is now fully blocked, preventing any further probing or communication with the destination. The threat has been effectively contained. When a SOC analyst opens the Sentinel incident, they see that containment has already occurred: the malicious IP was identified, the IP Group was updated, and the firewall block is in effect — all with a full audit trail of every automated action taken, from detection through response. No manual intervention was required. Conclusion With these five new IDPS detections, Azure Firewall closes the gap between network-level signal and SOC-level action. Raw signature telemetry is automatically transformed into severity-aware, MITRE ATT&CK-mapped alerts inside Microsoft Sentinel and Microsoft Defender XDR — giving security teams correlated, investigation-ready incidents instead of isolated log entries. Combined with automation playbooks, the result is a fully integrated detect-and-respond workflow: Azure Firewall identifies malicious behavior, Sentinel raises and enriches the incident, and a Logic App playbook contains the threat by updating firewall policy in real time — all without manual intervention. These detections are included at no additional cost. Simply install the Azure Firewall solution from the Microsoft Sentinel Content Hub, and the analytic rules automatically appear in your Sentinel workspace — ready to enable, customize, and operationalize. Get started today: Azure Firewall with Microsoft Sentinel overview Automate Threat Response with Playbooks in Microsoft Sentinel Azure Firewall Premium features implementation guide Recent real‑world breaches underscore why these detections matter. Over the past year, attackers have repeatedly gained initial access by exploiting public‑facing applications, followed by command‑and‑control activity, web shell deployment, cryptomining, and denial‑of‑service attacks. Incidents such as the GoAnywhere MFT exploitation, widespread web‑application intrusions observed by Cisco Talos, and large‑scale cryptomining campaigns against exposed cloud services demonstrate the value of correlating repeated network‑level malicious signals. The new Azure Firewall IDPS detections are designed to surface these patterns early, reduce alert noise, and feed high‑confidence network signals directly into Microsoft Sentinel and Microsoft Defender XDR for faster investigation and response. Your network telemetry is a first-class security signal - let it work for you! Visit us at RSA 2026 to see the full detection-to-containment workflow live.
Help! - How is VNet traffic reaching vWAN/on‑prem when the VNet isn’t connected to the vWAN hub
Hello, I needed some clarity on how the following is working: Attached is a network diagram of our current setup. The function apps (in VNet-1) initiate a connection(s) to a specific IP:Port or FQDN:Port in the on-premises network(s). A Private DNS zone ensures that any FQDN is resolved to the correct internal IP address of the on-prem endpoint. In our setup, both the function app and the external firewall reside in the same VNet. This firewall is described as “Unattached” because it is not the built-in firewall of a secured vWAN hub, but rather an independent Azure Firewall deployed in that VNet. The VNet has a user-defined default route (0.0.0.0/0) directing all outbound traffic to the firewall’s IP. The firewall then filters the traffic, allowing only traffic destined to whitelisted on-premises IP: Port or FQDN: Port combinations (using IP Groups), and blocking everything else. The critical question and the part that I am unable to figure out is: Once the firewall permits a packet, how does Azure know to route it to the vWAN hub and on to the site-to-site VPN? Because VNet-1 truly has no connection at all to the vWAN hub (no direct attachment, no peering, no VPN from the NVA). But the traffic is still reaching the on-prem sites. Unable to figure out how this is happening. Am I missing something obvious? Any help on this would be appreciated. Thank you!
Traffic processing BGP Azure VPN gateway A/A
Hello, Can someone explain how Azure processes the traffic with implemented a VPN gateway in Active Active mode?. Azure firewall premium is also configured. BGP is without preferences. The user route definition is set up to the next hop Azure firewall . Is it possible in this scenario occurs the asymmetric routing with traffic drop by azure firewall ? In my understand is that, if we need to configure User route definition on Gateway subnet to inspect traffic to peering subnet, so the firewall don't see traffic passing through VPN gateway. Traffic going through ipsec tunnels can go different paths and firewall do not interfere because everything is routed to it by user route definition.Zero Trust with Azure Firewall, Azure DDoS Protection and Azure WAF: A practical use case
Introduction Zero Trust has emerged as the defining security ethos of the modern enterprise. It is guided by a simple but powerful principle: “Never trust, always verify.” This principle is more relevant now than ever as cyberattacks continue to trend upward in both frequency and impact, affecting organizations of every size and industry. No entity large or small can assume immunity. As a result, adopting Zero Trust is no longer optional, it is a foundational requirement for designing secure, resilient architectures. A key tenet of Zero Trust is the assumption of breach, thus designing systems with the expectation that threats may already exist both outside and inside the network perimeter. To implement this principle, you need multiple, independent security controls that inspect traffic at different layers and enforce least privilege access continuously. Relying on a single security control, even a highly capable one, leaves gaps that modern attackers are adept at exploiting. It is within this context that combining the use of Azure Firewall, Azure DDoS Protection and Azure Web Application Firewall (WAF) services to secure Web Applications while protecting the network perimeter becomes important. Together, these services deliver comprehensive protection across the network and application layers. Defense-in-depth: Why Azure WAF, Azure DDoS Protection and Azure Firewall are essential for Zero Trust In these sections ahead, we examine the common network and application-layer attack vectors that target modern web applications and illustrate how Azure WAF, Azure DDoS protection, and Azure Firewall, when layered strategically, work in tandem to mitigate these threats. The architecture The test environment was designed to reflect a common Azure deployment pattern: Azure DDoS Protection at the edge, to defend against a comprehensive set of network layer (layer 3/4) attacks Azure Application Gateway with WAF, inspecting inbound HTTP traffic for application-layer threats Azure Firewall Premium behind the gateway, providing network-layer protection, deep packet inspection, and outbound traffic governance. A backend subnet hosting an intentionally vulnerable application (OWASP Juice Shop) to simulate real-world attack scenarios. Traffic flows through the DDoS first, then WAF, and then the firewall, before reaching the backend. Outbound traffic from the backend is routed through the firewall for inspection. This ensures that all inbound and outbound traffic is scrutinized. Two access paths that will be tested: Via the Application Gateway public IP, where traffic passes through DDoS, WAF and Firewall. Via the Firewall public IP using a DNAT rule, where traffic bypasses WAF and is inspected only by the Firewall. The following scenarios illustrate how this complementary protection strengthens overall resilience: Scenario 1: SQL injection (application-layer attack) Let’s say an attacker on the internet attempts to access the application’s login endpoint via the Application Gateway IP address and injects a SQL payload into the input field. For example, the attacker submits a request containing the following payload in the User ID field: ?id=' OR 1=1 -- Azure WAF will receive the request, analyze, and if Azure WAF is deployed in Prevention mode, it will immediately detect the SQL injection attempt using its built-in Managed Ruleset. Upon detection, Azure WAF will return a WAF block page, preventing the request from ever reaching the application. By contrast, when the same application is accessed through a firewall-only path (for example, via a DNAT rule on Azure Firewall that exposes the application on port 443), Azure Firewall allows the traffic as it does not perform deep Application layer inspection and SQL injection payloads when embedded within the HTTP request body, appear legitimate at the network layer. Here is a snapshot of the attacker gaining access to the admin role when they insert this SQL injection attack without Azure WAF and only Azure Firewall in the path. Scenario 2: Volumetric and application-layer DDoS attacks Next, the attacker launches a volumetric network layer DDoS (SYN/UDP floods) to saturate bandwidth, but Azure DDoS Network Protection absorbs and scrubs the attack at the edge, so no traffic reaches Application Gateway, WAF, or Firewall. When the network layer attack fails, they shift to HTTP flood attack at the application layer, overwhelming the web application with a high volume of requests. Some requests include exploit attempts, while others are designed purely to exhaust application resources. Azure WAF here, can identify malicious patterns such as: Automated bots lacking proper headers Abnormal request rates Known exploit payloads embedded within requests Malicious IP addresses Note: Azure DDoS Protection is a comprehensive service that provides protection across network layers (Layer 3 and 4), while HTTP DDoS Protection specifically targets application-layer attacks (Layer 7) and is integrated with Azure WAF. They are complementary services designed to defend against different types of threats within the Azure environment. Additionally, if the botnet’s IPs are known threat actors or malicious traffic, Azure Firewall’s threat intelligence and IDPS will be able to flag this traffic too. Together, these services form a complementary, defense-in-depth strategy for protecting Azure workloads against distributed denial-of-service attacks. Scenario 3: Path Traversal Attempt/Information leak: (Application-Layer Attack) Next, the attacker sends HTTP requests to access sensitive system files such as /etc/passwd by sending crafted HTTP requests to the application via the Application Gateway public IP address. The request successfully passes through Azure Application Gateway WAF, as it does not trigger a managed rule violation in this case. However, when the request reaches Azure Firewall, the Firewall’s IDPS detects the malicious pattern in the HTTP header and blocks the connection before it can reach the backend workload. Because the backend connection is denied by Azure Firewall, Application Gateway is unable to establish a successful response and returns a 504 Gateway Timeout to the client, rather than a 403 Forbidden response that would typically be generated by WAF when it blocks traffic. Below is the log from Azure Firewall showing that its able to detect this traffic as – Attempted Information Leak. As seen below, the traffic passed Application Gateway+WAF but was caught by Azure Firewall: This scenario highlights an important architectural outcome: The combination of WAF and Azure Firewall provides layered enforcement, even if an attack manages to slip past Azure WAF, Azure Firewall adds an additional enforcement layer to ensure the application remains protected. Now, let’s look at some more Network Layer attacks: Scenario 4: Network reconnaissance and breach In this scenario, port 3389 is exposed on Application Gateway using the L4 TCP Proxy option. Now, the attacker attempts to scan the Application Gateway on all the ports/protocols and found that port 3389 was open along with other ports such as ports 80, 8080, 3000. Azure WAF will alert us for Layer 7/Application exploit but cannot verify/validate the attack on port 3389 since it was purely Layer 3/4 and contained no HTTP payload for WAF inspection. The L4 proxy listener on App Gateway simply forwards the raw TCP connections to the Azure Firewall behind it. Azure Firewall, however, performs full network‑layer inspection across all ports and protocols, allowing it to detect and alert on this type of L3/L4 reconnaissance even when App Gateway had the port open via the TCP proxy feature. As seen below the traffic passed Application Gateway+WAF but was caught by Azure Firewall since it is non-HTTP: The attacker then tries a different approach: Now the attacker somehow compromises a workstation inside our network and attempts to move laterally to the web server via RDP on port 3389 and/or attempts to exfiltrate and try to access something outside of the network. Azure Firewall located inside the VNet blocks the RDP attempt (if there is no rule allowing it) and if there is, its IDPS flags/blocks the traffic as suspicious. In this case, Azure WAF will not be involved but Azure Firewall inspects this internal and/or outbound traffic and blocks it. This illustrates how a combination of the two stops the attacker at multiple points: firewall foiled the reconnaissance and lateral movement/exfiltration, WAF foiled the application exploit. We can see below the outbound malicious attempt caught by Azure Firewall IDPS: In summary, Azure WAF is like the “bodyguard at the application’s front door” – inspecting every HTTP request in detail and ejecting those carrying hidden weapons or exhibiting bad behavior. It focuses on the web layer, which Azure Firewall or DDoS alone cannot fully protect. If we only had the WAF and no network firewall or DDoS, we’d be safe from many web attacks but would remain exposed to network-level threats (e.g., someone trying to RDP into a VM, or flooding a non-HTTP service). Conversely, if we had only the firewall, a crafty attacker could still exploit a vulnerability in our web app with a well-crafted HTTP request that looks “allowed” to the firewall – that’s where the WAF comes in to catch it. Azure Firewall on the other hand, acts as the “moat and drawbridge” to your cloud network: it keeps out the obvious bad guys at the gate, tightly limits what’s allowed in or out (no implicit trust for internal IPs), and uses threat intel + signatures to sniff out known threats in any traffic it passes, even outbound traffic. The table below shows the traffic flow that will be filtered by Azure WAF vs Azure Firewall. As you can see, layered security is fundamental to Zero Trust Conclusion In a Zero Trust architecture, security cannot rely on implicit trust or a single layer of defense. The combination of Azure Firewall Premium, Azure DDoS protection and Azure Application Gateway WAF exemplifies defense-in-depth by protecting both network and application layers. Organizations hosting internet-facing applications should adopt this layered strategy to reduce exposure to modern threats, prevent lateral movement, and maintain strict control over outbound traffic. By implementing these services together, you align with Microsoft’s recommended best practices for Zero Trust and significantly strengthen your cloud security posture. References: Implement a Zero Trust network for web applications by using Azure Firewall and Azure Application Gateway What is Azure Web Application Firewall? Azure DDoS Protection Overview | Microsoft Learn What is Azure Firewall? Architecture designs using Azure WAF and Azure Firewall together Zero Trust Assessment Overview | Microsoft Learn
How to find Azure Firewall SNAT exhaustion on a compute unit?
I have some applications on my AKS cluster which frequently hits a application server. This application server URL is behind Akamai. When ever applications want to establish an SSL connection with the external URL, it has to go through Azure Firewall. I have occasional connection timeouts if a connection is not establish to Akamai servers in 1s. I saw that the SNAT Utilization is in the range of 10 percent to 30%. I know this graph is smoothened out across instances and can't see which Azure Firewall compute unit is getting overloaded if I have frequent access to one URL which goes through Akamai? Is there any way to find out the reason for these occasional connection timeouts with the external IPs(Akamai)? through logs or by any other means? I believe lack of the SNAT metrics by firewall compute unit is responsible for such tough debugging.How Azure network security can help you meet NIS2 compliance
With the adoption of the NIS2 Directive EU 2022 2555, cybersecurity obligations for both public and private sector organizations have become more strict and far reaching. NIS2 aims to establish a higher common level of cybersecurity across the European Union by enforcing stronger requirements on risk management, incident reporting, supply chain protection, and governance. If your organization runs on Microsoft Azure, you already have powerful services to support your NIS2 journey. In particular Azure network security products such as Azure Firewall, Azure Web Application Firewall WAF, and Azure DDoS Protection provide foundational controls. The key is to configure and operate them in a way that aligns with the directive’s expectations. Important note This article is a technical guide based on the NIS2 Directive EU 2022 2555 and Microsoft product documentation. It is not legal advice. For formal interpretations, consult your legal or regulatory experts. What is NIS2? NIS2 replaces the original NIS Directive 2016 and entered into force on 16 January 2023. Member states must transpose it into national law by 17 October 2024. Its goals are to: Expand the scope of covered entities essential and important entities Harmonize cybersecurity standards across member states Introduce stricter supervisory and enforcement measures Strengthen supply chain security and reporting obligations Key provisions include: Article 20 management responsibility and governance Article 21 cybersecurity risk management measures Article 23 incident notification obligations These articles require organizations to implement technical, operational, and organizational measures to manage risks, respond to incidents, and ensure leadership accountability. Where Azure network security fits The table below maps common NIS2 focus areas to Azure network security capabilities and how they support compliance outcomes. NIS2 focus area Azure services and capabilities How this supports compliance Incident handling and detection Azure Firewall Premium IDPS and TLS inspection, Threat Intelligence mode, Azure WAF managed rule sets and custom rules, Azure DDoS Protection, Azure Bastion diagnostic logs Detect, block, and log threats across layers three to seven. Provide telemetry for triage and enable response workflows that are auditable. Business continuity and resilience Azure Firewall availability zones and autoscale, Azure Front Door or Application Gateway WAF with zone redundant deployments, Azure Monitor with Log Analytics, Traffic Manager or Front Door for failover Improve service availability and provide data for resilience reviews and disaster recovery scenarios. Access control and segmentation Azure Firewall policy with DNAT, network, and application rules, NSGs and ASGs, Azure Bastion for browser based RDP SSH without public IPs, Private Link Enforce segmentation and isolation of critical assets. Support Zero Trust and least privilege for inbound and egress. Vulnerability and misconfiguration defense Azure WAF Microsoft managed rule set based on OWASP CRS. Azure Firewall Premium IDPS signatures Reduce exposure to common web exploits and misconfigurations for public facing apps and APIs. Encryption and secure communications TLS policy: Application Gateway SSL policy; Front Door TLS policy; App Service/PaaS minimum TLS. Inspection: Azure Firewall Premium TLS inspection Inspect and enforce encrypted communication policies and block traffic that violates TLS requirements. Inspect decrypted traffic for threats. Incident reporting and evidence Azure Network Security diagnostics, Log Analytics, Microsoft Sentinel incidents, workbooks, and playbooks Capture and retain telemetry. Correlate events, create incident timelines, and export reports to meet regulator timelines. NIS2 articles in practice Article 21 cybersecurity risk management measures Azure network controls contribute to several required measures: Prevention and detection. Azure Firewall blocks unauthorized access and inspects traffic with IDPS. Azure DDoS Protection mitigates volumetric and protocol attacks. Azure WAF prevents common web exploits based on OWASP guidance. Logging and monitoring. Azure Firewall, WAF, DDoS, and Bastion resources produce detailed resource logs and metrics in Azure Monitor. Ingest these into Microsoft Sentinel for correlation, analytics rules, and automation. Control of encrypted communications. Azure Firewall Premium provides TLS inspection to reveal malicious payloads inside encrypted sessions. Supply chain and service provider management. Use Azure Policy and Defender for Cloud to continuously assess configuration and require approved network security baselines across subscriptions and landing zones. Article 23 incident notification Build an evidence friendly workflow with Sentinel: Early warning within twenty four hours. Use Sentinel analytics rules on Firewall, WAF, DDoS, and Bastion logs to generate incidents and trigger playbooks that assemble an initial advisory. Incident notification within seventy two hours. Enrich the incident with additional context such as mitigation actions from DDoS, Firewall and WAF. Final report within one month. Produce a summary that includes root cause, impact, and corrective actions. Use Workbooks to export charts and tables that back up your narrative. Article 20 governance and accountability Management accountability. Track policy compliance with Azure Policy initiatives for Firewall, DDoS and WAF. Use exemptions rarely and record justification. Centralized visibility. Defender for Cloud’s network security posture views and recommendations give executives and owners a quick view of exposure and misconfigurations. Change control and drift prevention. Manage Firewall, WAF, and DDoS through Network Security Hub and Infrastructure as Code with Bicep or Terraform. Require pull requests and approvals to enforce four eyes on changes. Network security baseline Use this blueprint as a starting point. Adapt to your landing zone architecture and regulator guidance. Topology and control plane Hub and spoke architecture with a centralized Azure Firewall Premium in the hub. Enable availability zones. Deploy Azure Bastion Premium in the hub or a dedicated management VNet; peer to spokes. Remove public IPs from management NICs and disable public RDP SSH on VMs. Use Network Security Hub for at-scale management. Require Infrastructure as Code for all network security resources. Web application protection Protect public apps with Azure Front Door Premium WAF where edge inspection is required. Use Application Gateway WAF v2 for regional scenarios. Enable the Microsoft managed rule set and the latest version. Add custom rules for geo based allow or deny and bot management. enable rate limiting when appropriate. DDoS strategy Enable DDoS Network Protection on virtual networks that contain internet facing resources. Use IP Protection for single public IP scenarios. Configure DDoS diagnostics and alerts. Stream to Sentinel. Define runbooks for escalation and service team engagement. Firewall policy Enable IDPS in alert and then in alert and deny for high confidence signatures. Enable TLS inspection for outbound and inbound where supported. Enforce FQDN and URL filtering for egress. Require explicit allow lists for critical segments. Deny inbound RDP SSH from the internet. Allow management traffic only from Bastion subnets or approved management jump segments. Logging, retention, and access Turn on diagnostic settings for Firewall, WAF, DDoS, and Application Gateway or Front Door. Send to Log Analytics and an archive storage account for long term retention. Set retention per national law and internal policy. Azure Monitor Log Analytics supports table-level retention and archive for up to 12 years, many teams keep a shorter interactive window and multi-year archive for audits. Restrict access with Azure RBAC and Customer Managed Keys where applicable. Automation and playbooks Build Sentinel playbooks for regulator notifications, ticket creation, and evidence collection. Maintain dry run versions for exercises. Add analytics for Bastion session starts to sensitive VMs, excessive failed connection attempts, and out of hours access. Conclusion Azure network security services provide the technical controls most organizations need in order to align with NIS2. When combined with policy enforcement, centralized logging, and automated detection and response, they create a defensible and auditable posture. Focus on layered protection, secure connectivity, and real time response so that you can reduce exposure to evolving threats, accelerate incident response, and meet NIS2 obligations with confidence. References NIS2 primary source Directive (EU) 2022/2555 (NIS2). https://eur-lex.europa.eu/eli/dir/2022/2555/oj/eng Azure Firewall Premium features (TLS inspection, IDPS, URL filtering). https://learn.microsoft.com/en-us/azure/firewall/premium-features Deploy & configure Azure Firewall Premium. https://learn.microsoft.com/en-us/azure/firewall/premium-deploy IDPS signature categories reference. https://learn.microsoft.com/en-us/azure/firewall/idps-signature-categories Monitoring & diagnostic logs reference. https://learn.microsoft.com/en-us/azure/firewall/monitor-firewall-reference Web Application Firewall WAF on Azure Front Door overview & features. https://learn.microsoft.com/en-us/azure/frontdoor/web-application-firewall WAF on Application Gateway overview. https://learn.microsoft.com/en-us/azure/web-application-firewall/overview Examine WAF logs with Log Analytics. https://learn.microsoft.com/en-us/azure/application-gateway/log-analytics Rate limiting with Front Door WAF. https://learn.microsoft.com/en-us/azure/web-application-firewall/afds/waf-front-door-rate-limit Azure DDoS Protection Service overview & SKUs (Network Protection, IP Protection). https://learn.microsoft.com/en-us/azure/ddos-protection/ddos-protection-overview Quickstart: Enable DDoS IP Protection. https://learn.microsoft.com/en-us/azure/ddos-protection/manage-ddos-ip-protection-portal View DDoS diagnostic logs (Notifications, Mitigation Reports/Flows). https://learn.microsoft.com/en-us/azure/ddos-protection/ddos-view-diagnostic-logs Azure Bastion Azure Bastion overview and SKUs. https://learn.microsoft.com/en-us/azure/bastion/bastion-overview Deploy and configure Azure Bastion. https://learn.microsoft.com/en-us/azure/bastion/tutorial-create-host-portal Disable public RDP and SSH on Azure VMs. https://learn.microsoft.com/en-us/azure/virtual-machines/security-baseline Azure Bastion diagnostic logs and metrics. https://learn.microsoft.com/en-us/azure/bastion/bastion-diagnostic-logs Microsoft Sentinel Sentinel documentation (onboard, analytics, automation). https://learn.microsoft.com/en-us/azure/sentinel/ Azure Firewall solution for Microsoft Sentinel. https://learn.microsoft.com/en-us/azure/firewall/firewall-sentinel-overview Use Microsoft Sentinel with Azure WAF. https://learn.microsoft.com/en-us/azure/web-application-firewall/waf-sentinel Architecture & routing Hub‑spoke network topology (reference). https://learn.microsoft.com/en-us/azure/architecture/networking/architecture/hub-spoke Azure Firewall Manager & secured virtual hub. https://learn.microsoft.com/en-us/azure/firewall-manager/secured-virtual-hub
Spoke-Hub-Hub Traffic with VPN Gateway BGP and Firewall Issue
Hello, I’m facing a situation where I’m trying to have Azure Firewall Inspection on the VPN Gateway VNET-VNET Connectivity. It seems to work if I go from SpokeA-HubAFirewall-HubAVPN—HubBVPN-SpokeB but if I try to go from SpokeA-HubAFirewall-HubAVPN-HubBVM or Inbound Resolver it fails to route correctly according to Connectivity Troubleshooter it stops at HubAVPN with Local Error: RouteMissing but then reaches destination health so makes me believe it’s getting there but not following the route I want it to take which might be causing routing issues. What Am I missing here? This connectivity was working before introducing the Azure Firewall for Inspection with the UDR. Is what I’m trying to accomplish not possible? I’ve tried different types of UDR rules on the Gateway Subnet, and this is my most recent configuration. The reason I’m trying to accomplish this is because I’m seeing a similar error in our Hub-Spoke Hybrid environment and I’m trying to replicate the issue. Current Configuration 2x Hubs with Spoke networks attached so example Hub-Spoke-A Configuration: Hub-A Contains following subnets and Resources VPN Gateway - GateWaySubnet Azure Firewall - AzureFirewallSubnet Inbound Private Resolver - PrivateResolverSubnet Virtual Machine – VM Subnet Gateway Subnet has an attached UDR with the following routes Propagation - True Prefix Destination – Hub-B Next Hop Type – Virtual Appliance Next Hope IP – Hub-A Firewall Prefix Destination – Spoke-B Next Hop Type – Virtual Appliance Next Hope IP – Hub-A Firewall Hub-Spoke-B Configuration: Hub-B Contains following subnets and Resources VPN Gateway - GateWaySubnet Azure Firewall - AzureFirewallSubnet Inbound Private Resolver - PrivateResolverSubnet Virtual Machine – VM Subnet Gateway Subnet has an attached UDR with the following Routes Propagation - True Prefix Destination – Hub-A Next Hop Type – Virtual Appliance Next Hope IP – Hub-B Firewall Prefix Destination – Spoke-A Next Hop Type – Virtual Appliance Next Hope IP – Hub-B Firewall Spoke Subnets has an attached UDR with the following Routes Propagation - True Prefix Destination – 0.0.0.0/0 Next Hop Type – Virtual Appliance Next Hope IP – HubA/HubB Firewall (Depending on what hub its peered to) VPN Gateways HA VNET-VNET with BGP Enabled. I can see that it knows the routes and like I said this was working prior introducing the UDRs for force traffic through the azure firewall.
