cdncheck: Why Identifying CDNs and WAFs Matters for Security Reconnaissance

Hook

Scanning a vulnerability you found only to realize you've been hammering Cloudflare's edge servers for the past hour? You're not testing the origin—you're testing someone else's infrastructure.

Context

Security researchers and bug bounty hunters face a fundamental problem: modern web infrastructure is layered. A domain might resolve to an IP address, but that IP could belong to Cloudflare, AWS CloudFront, Akamai, or dozens of other CDN and WAF providers. Attempting to exploit vulnerabilities against these intermediary services is not only ineffective—it wastes time, triggers rate limits, and provides zero insight into the actual origin server's security posture.

Traditionally, identifying this infrastructure required manual WHOIS lookups, ASN database queries, or familiarity with provider IP ranges. Some tools exist—commercial IP intelligence APIs like ipinfo.io or MaxMind—but they're either paid services or not specifically designed for security workflows. ProjectDiscovery's cdncheck fills this gap: a purpose-built utility that maintains an aggregated database of CDN, cloud provider, and WAF infrastructure, enabling instant detection during reconnaissance. Whether you're building automated scanning pipelines or performing manual assessments, knowing what sits between you and your target fundamentally changes your approach.

Technical Insight

cdncheck's architecture revolves around a compiled index of provider infrastructure mappings. The tool aggregates data from three primary sources: static CIDR blocks, Autonomous System Numbers (ASNs), and CNAME domain patterns. These are defined in YAML configuration files under the sources/ directory, where each provider (Cloudflare, Fastly, AWS, etc.) lists their IP ranges, ASN assignments, or characteristic domains. During build time, a generator processes these YAML files and produces sources_data.json—a unified index that ships with the binary.

When you check an IP address, cdncheck performs multiple detection methods simultaneously. First, it attempts IP range matching using Go's net package primitives, checking if the target IP falls within any provider's CIDR blocks. Second, it can perform ASN lookups if configured with an ASN database. Third, for domain-based checks, it resolves CNAMEs and matches them against known provider patterns. Here's how you'd use it as a library:

package main

import (
    "fmt"
    "github.com/projectdiscovery/cdncheck"
)

func main() {
    client := cdncheck.New()
    
    // Check if an IP belongs to a CDN/cloud provider
    matched, val, err := client.Check("1.1.1.1")
    if err != nil {
        panic(err)
    }
    
    if matched {
        fmt.Printf("Detected: %s (Type: %s)\n", val, client.CheckCDN("1.1.1.1"))
    } else {
        fmt.Println("Not a known CDN/cloud IP")
    }
    
    // Check using domain CNAME
    isCDN, provider, err := client.CheckDomainWithFallback("example.com")
    if isCDN {
        fmt.Printf("Domain uses: %s\n", provider)
    }
}

The library design is intentionally lightweight. The Check() method returns a boolean match status, the provider name, and an error—simple enough to integrate into existing toolchains. For CLI usage, cdncheck supports multiple input methods: individual IPs via flags, domain resolution with -i flag, or bulk processing from stdin with optional JSON/JSONL output formatting.

What makes cdncheck particularly useful for security workflows is its filtering capabilities. The -type flag lets you filter results by infrastructure category (cdn, waf, cloud), and -match or -filter flags allow provider-specific targeting. This becomes powerful in automation scenarios—imagine a reconnaissance pipeline that identifies all Cloudflare-protected domains, skips them for certain vulnerability classes (like rate-limit-sensitive tests), but flags them for origin IP discovery techniques.

The provider data extensibility is another architectural win. Adding a new CDN or cloud provider doesn't require code changes—just update the YAML configuration with the provider's IP ranges, ASNs, or CNAME patterns. The configuration supports fetching ranges from URLs (many providers publish their IP ranges as downloadable files), direct CIDR block listings, or ASN assignments. This separation of detection logic from provider data means the tool remains relevant as the infrastructure landscape evolves.

Under the hood, IP range matching uses net.ParseCIDR() and net.IPNet.Contains() for efficient lookups. While not as optimized as specialized data structures like radix trees, the performance is acceptable for reconnaissance workloads where you're checking hundreds or thousands of IPs rather than millions. The tool also integrates with ProjectDiscovery's retryabledns library for robust DNS resolution, handling timeouts and retries gracefully—critical when checking large domain lists where DNS infrastructure might be flaky.

Gotcha

The biggest limitation is data freshness. CDN providers constantly expand their infrastructure, acquire new IP ranges, and adjust ASN allocations. cdncheck's detection accuracy is only as current as its compiled sources_data.json index. Unlike commercial IP intelligence services that update continuously, cdncheck requires you to update the tool itself to get refreshed provider data. If you're running a months-old version, you'll miss newly allocated IP ranges—potentially misidentifying infrastructure or missing CDN detection entirely.

There's no auto-update mechanism for the provider database. The tool doesn't check for updated provider ranges at runtime or download fresh data periodically. For security teams relying on cdncheck in production pipelines, this means establishing a cadence for updating the tool—weekly or monthly depending on accuracy requirements. This is less "set and forget" than using an API-based service.

Detection is also limited to network-layer visibility. If a target uses application-layer proxying, reverse proxies with non-provider IP space, or sophisticated traffic routing through generic hosting providers, cdncheck won't identify it. The tool assumes providers use identifiable infrastructure—their own IP ranges, ASNs, or CNAME patterns. Stealthy proxy configurations that deliberately avoid these fingerprints will evade detection. Additionally, CNAME-based detection relies on DNS resolution working correctly; DNS-level blocking, private resolvers, or non-standard configurations can cause false negatives.

Verdict

Use if: You're building security reconnaissance pipelines that need fast, offline CDN/WAF detection to adjust scanning strategies, performing bug bounty work where identifying infrastructure type informs your testing approach, or integrating provider detection into custom tooling without API rate limits or costs. The library interface makes it trivial to embed in Go-based security tools, and the provider-agnostic configuration means you can extend it for niche or regional providers. Skip if: You need guaranteed up-to-date provider data without manual maintenance overhead (use a commercial IP intelligence API instead), require application-layer proxy detection beyond basic infrastructure fingerprinting, or work in environments where a simple ASN lookup or WHOIS query suffices. cdncheck excels at what it does—fast, purpose-built infrastructure identification—but only if you're willing to keep it current.