HTTP DDoS protection rule set is enabled in Azure Front Door WAF

Overview

Azure Front Door Web Application Firewall (WAF) offers the Microsoft HTTP DDoS ruleset, a managed rule set that provides automated layer 7 protection against volumetric HTTP-based attacks at Microsoft’s global edge network. Threat actors increasingly bypass network-layer DDoS defenses by generating HTTP floods, slowloris-style connection exhaustion, and high-frequency requests from distributed botnets that resemble legitimate traffic just enough to defeat static IP allow/block lists and fixed-threshold rate limiting rules. The HTTP DDoS ruleset closes this gap by continuously baselining normal request volume for each Azure Front Door profile and learning both a global profile-level threshold and a per-client-IP threshold; once a profile-wide surge indicates an attack, the ruleset throttles the specific IP addresses driving the anomaly without requiring administrators to pre-configure static limits. The ruleset’s two rules — 500100, which detects anomalous request rates across the profile, and 500110, which applies stricter thresholds to traffic that Microsoft Threat Intelligence classifies as bot activity — are evaluated before any custom rules or other managed rule sets, so volumetric abuse is throttled at the edge before it can exhaust origin compute, database connections, or application threads. Without this ruleset enabled, an attacker can sustain a high-rate HTTP flood or coordinated bot swarm against an Azure Front Door-fronted application until backend capacity is exhausted, denying service to legitimate users, because the fixed-threshold controls available elsewhere in the WAF policy do not adapt to attack conditions in real time.

Remediation

• HTTP DDoS Ruleset (Preview) - Front Door WAF
• What is Azure Web Application Firewall on Azure Front Door?
• Create a Web Application Firewall policy for Azure Front Door using the Azure portal
• Azure DDoS Protection overview

Run it

The check runs as part of the whole assessment, with the ZeroTrustAssessment module installed:

Install-Module ZeroTrustAssessment -Scope CurrentUser
Connect-Maester
Invoke-Maester -Pack ZTA -SkipBuiltIn

Leave out -SkipBuiltIn to run Maester’s own checks in the same run.

About this check

Severity	High
Effort to fix	Low
Impact on users	Low
Pillar	Network
Category	Azure Network Security
Product	Azure
Feature	Network security
Area	Infrastructure hardening
ATT&CK	T1499.002 Service Exhaustion Flood, T1499.003 Application Exhaustion Flood
Licence	Consumption-based: Azure WAF on Azure Front Door Premium
Tenant	Workforce

Product, feature, area and ATT&CK are Maester’s: the assessment does not record them, so Maester keeps them in the pack’s taxonomy.json.

A Microsoft check, part of the Zero Trust Assessment pack. Text from ZeroTrustAssessment 3.1.0, © Microsoft, MIT licence.