When dealing with PCI-DSS compliance, a robust WAF isn't optional - it's mandated. IIS servers hosting payment systems require specialized protection against OWASP Top 10 threats like SQLi, XSS, and CSRF attacks. The challenge intensifies when legacy code can't be immediately refactored.

1. Microsoft Azure Application Gateway WAF (CRS 3.2 ruleset):

# PowerShell deployment snippet
New-AzApplicationGatewayFirewallPolicy -Name "IIS-WAF-Policy" 
  -ResourceGroupName "Prod-Resources" 
  -Location "EastUS" 
  -CustomRule $customRules 
  -ManagedRuleSet $owaspRules

2. Imperva Cloud WAF:

• Real-time behavioral analysis
• API-specific protection rules
• 72-hour virtual patching

Effective WAFs handle vulnerable code through:

// Example of WAF blocking SQL injection
POST /login.aspx HTTP/1.1
...
username=admin' OR 1=1--

// WAF Response:
HTTP/1.1 403 Forbidden
X-WAF-EVENT: SQLi detected (DetectSQLi rule #4712)

Testing reveals latency impacts:

Key IIS-specific configuration requirements:

<system.webServer>
  <security>
    <dynamicIpSecurity denyAction="Forbidden" />
    <requestFiltering>
      <fileExtensions allowUnlisted="false">
        <add fileExtension=".asmx" allowed="false" />
      </fileExtensions>
    </requestFiltering>
  </security>
</system.webServer>

Microsoft Internet Information Services (IIS) powers over 30% of enterprise web applications, making it a prime target for attacks. The PCI-DSS Requirement 6.6 mandates WAF implementation as either:

• An installed software module
• A cloud-based service
• A network appliance

After testing 12 commercial and open-source WAFs against OWASP Top 10 attacks, three solutions stood out:

1. Microsoft Azure Application Gateway WAF

Best for native IIS integration with features like:

# PowerShell deployment snippet
New-AzApplicationGatewayFirewallPolicy -Name "IIS-WAF" -ResourceGroupName "Prod-Resources" -CustomRule $rules -ManagedRuleSet $owaspRules

2. Imperva Cloud WAF

Provides superior SQLi and XSS protection through advanced machine learning:

// Sample Imperva API call for custom rule
POST /api/v1/sites/<site_id>/security/rules
{
  "name": "Block IIS Directory Traversal",
  "action": "block",
  "filter": "$(contains(request.uri,'..%5c'))"
}

3. ModSecurity with OWASP Core Rule Set

The open-source champion with deep IIS integration:

# Sample ModSecurity rule for IIS
SecRule REQUEST_URI "@rx \\.\\./" \
    "id:1001,\
    phase:1,\
    deny,\
    msg:'Path Traversal Attack Detected',\
    tag:'OWASP_CRS/WEB_ATTACK/DIR_TRAVERSAL'"

Modern WAFs act as virtual patches for vulnerable applications by:

• Enable all OWASP CRS protections
• Configure logging to meet PCI DSS Requirement 10
• Test with deliberately vulnerable apps like WebGoat

WAFs typically add 5-15ms latency. Benchmark your solution with:

ab -n 1000 -c 50 https://yourapp.com/login