//! Stress test demonstrating DNS rebinding SSRF bypass vulnerability.
#![allow(
    clippy::cast_precision_loss,
    clippy::cast_possible_truncation,
    clippy::cast_sign_loss,
    clippy::too_many_lines,
    clippy::manual_flatten
)]
//!
//! **VULNERABILITY FOUND**: Time-Of-Check-Time-Of-Use (TOCTOU) gap in DNS resolution.
//!
//! **ROOT CAUSE**:
//! - src/security/url_validation.rs:48-100 validates URL host (static check)
//! - But DNS resolution happens AFTER validation
//! - DNS can change between validation and actual request
//! - No re-validation of resolved IP address
//!
//! **Attack Sequence**:
//! 1. Attacker submits URL: <http://evil.com>
//! 2. Scanner validates: evil.com is not localhost/private ✓
//! 3. Attacker's DNS responds: evil.com → 1.2.3.4 (public IP)
//! 4. Scanner resolves DNS: evil.com → 1.2.3.4 ✓
//! 5. [TIME GAP - DNS TTL can be 0 seconds]
//! 6. Attacker's DNS rebinds: evil.com → 127.0.0.1
//! 7. Scanner connects: Uses stale DNS result OR re-resolves
//! 8. If re-resolved: Connects to 127.0.0.1 (SSRF bypass!)
//!
//! **DNS Rebinding Techniques**:
//! - Short TTL (0-1 seconds) to force frequent re-resolution
//! - Race condition: Change DNS between validation and connection
//! - Multiple A records: Return both public and private IPs
//!
//! **Real-World Example**:
//! - rebind.network (DNS rebinding service)
//! - Attacker uses: <http://7f000001.1.2.3.4.rebind.network>
//! - First resolution: 1.2.3.4 (public)
//! - Second resolution: 127.0.0.1 (localhost)
//! - Scanner bypasses SSRF check, accesses internal service
//!
//! **Impact**: SSRF bypass, access to internal services, cloud metadata APIs
//!
//! **Recommended Fix**:
//! - Resolve DNS during validation
//! - Cache resolved IP and reuse for connection
//! - Validate resolved IP is public
//! - Or: Validate IP AFTER resolution, before connection
//! - Implement DNS response pinning (use resolved IP, not hostname)

use std::net::{IpAddr, Ipv4Addr};

/// Documents the DNS rebinding attack vector.
///
/// This test explains how an attacker can bypass SSRF protection
/// using DNS rebinding with short TTLs.
#[tokio::test]
#[ignore] // Run with: cargo test --test stress_dns_rebinding -- --ignored --nocapture
async fn test_dns_rebinding_attack_scenario() {
    println!("=== DNS Rebinding SSRF Bypass Attack Scenario ===\n");

    println!("Attack setup:");
    println!("  Attacker controls DNS for evil.com");
    println!("  DNS server returns different IPs on successive queries");
    println!("  TTL set to 0 seconds (force re-resolution)");
    println!();

    println!("Timeline:");
    println!("  T=0ms:  User submits: http://evil.com");
    println!("  T=1ms:  Scanner validates URL (evil.com is not localhost) ✓");
    println!("  T=2ms:  Scanner resolves DNS → 1.2.3.4 (public IP)");
    println!("  T=3ms:  Validation passes (1.2.3.4 is public) ✓");
    println!("  T=4ms:  [DNS REBIND] Attacker changes DNS: evil.com → 127.0.0.1");
    println!("  T=5ms:  Scanner makes HTTP request...");
    println!("  T=6ms:  If re-resolved: Connects to 127.0.0.1 (SSRF!)");
    println!();

    println!("Current protection (src/security/url_validation.rs):");
    println!("  ✓ Validates URL scheme (http/https only)");
    println!("  ✓ Blocks localhost domain strings");
    println!("  ✓ Blocks private IP addresses in URL");
    println!("  ✗ Does NOT re-validate after DNS resolution");
    println!("  ✗ Does NOT pin resolved IP");
    println!();

    println!("VULNERABILITY: TOCTOU gap between validation and connection");
}

/// Simulates the validation vs. resolution timing gap.
///
/// Shows how DNS can change between URL validation and actual connection.
#[tokio::test]
#[ignore]
async fn test_dns_rebinding_timing_window() {
    use hickory_resolver::TokioResolver;
    use std::sync::Arc;

    println!("=== DNS Rebinding Timing Window Analysis ===\n");

    let resolver = Arc::new(
        TokioResolver::builder_tokio()
            .expect("Failed to create resolver builder")
            .build(),
    );

    // Simulate what happens during URL processing
    let url = "http://example.com";
    println!("Processing URL: {}", url);
    println!();

    // Step 1: URL validation (checks URL string only)
    println!("[Step 1] URL Validation:");
    let validation_start = std::time::Instant::now();
    let is_valid = validate_url_safe_simulation(url);
    let validation_elapsed = validation_start.elapsed();
    println!("  Result: {}", if is_valid { "PASS ✓" } else { "FAIL ✗" });
    println!("  Time: {}μs", validation_elapsed.as_micros());
    println!();

    // Step 2: DNS resolution (happens later, separate step)
    println!("[Step 2] DNS Resolution:");
    let dns_start = std::time::Instant::now();
    match resolver.lookup_ip("example.com").await {
        Ok(lookup) => {
            let dns_elapsed = dns_start.elapsed();
            let ips: Vec<IpAddr> = lookup.iter().collect();
            println!("  Resolved IPs: {:?}", ips);
            println!("  Time: {}ms", dns_elapsed.as_millis());
            println!();

            // Step 3: Gap between resolution and connection
            println!("[Step 3] Timing Gap:");
            println!("  Window: {}ms", dns_elapsed.as_millis());
            println!("  Risk: DNS can rebind during this window");
            println!("  With TTL=0: Attacker can change IP before connection");
            println!();
        }
        Err(e) => {
            println!("  Error: {}", e);
        }
    }

    println!("FINDING: Validation and resolution are separate steps");
    println!("DNS rebinding can occur in the timing gap");
}

/// Demonstrates multiple A record attack vector.
///
/// Attacker returns both public and private IPs in DNS response.
/// Depending on which IP is used, SSRF protection may be bypassed.
#[tokio::test]
#[ignore]
async fn test_dns_multiple_a_records_attack() {
    println!("=== Multiple A Record Attack Vector ===\n");

    println!("Attack technique:");
    println!("  Attacker's DNS returns multiple A records:");
    println!("    evil.com IN A 1.2.3.4      (public IP - passes validation)");
    println!("    evil.com IN A 127.0.0.1    (localhost - SSRF target)");
    println!("    evil.com IN A 192.168.1.1  (private IP - SSRF target)");
    println!();

    println!("Client behavior varies by implementation:");
    println!("  1. Some clients use FIRST IP (1.2.3.4 - safe)");
    println!("  2. Some clients ROUND-ROBIN (eventually hits 127.0.0.1)");
    println!("  3. Some clients try ALL IPs on failure (hits internal)");
    println!();

    println!("Scanner's behavior:");
    println!("  - URL validation only checks URL string");
    println!("  - DNS resolution returns all A records");
    println!("  - reqwest (HTTP client) chooses which IP to use");
    println!("  - No explicit IP validation after resolution");
    println!();

    println!("RISK: If HTTP client round-robins or retries with different IPs,");
    println!("internal/private IPs may be accessed despite URL validation");
}

/// Demonstrates cloud metadata API attack via DNS rebinding.
///
/// Common SSRF target: AWS metadata API at 169.254.169.254
#[tokio::test]
#[ignore]
async fn test_dns_rebinding_cloud_metadata_attack() {
    println!("=== Cloud Metadata API Attack via DNS Rebinding ===\n");

    println!("Target: AWS EC2 Metadata API");
    println!("  URL: http://169.254.169.254/latest/meta-data/");
    println!("  Purpose: Retrieve IAM credentials, instance metadata");
    println!();

    println!("Attack flow:");
    println!("  1. Attacker submits: http://evil.com/steal");
    println!("  2. First DNS query → 1.2.3.4 (public IP, passes validation)");
    println!("  3. Scanner starts HTTP request to evil.com");
    println!("  4. DNS rebinds → 169.254.169.254 (metadata API)");
    println!("  5. Scanner connects to metadata API");
    println!("  6. Attacker's initial response redirects to: /latest/meta-data/iam/...");
    println!("  7. Scanner follows redirect (within same domain)");
    println!("  8. Metadata API returns IAM credentials");
    println!();

    println!("Link-local addresses at risk:");
    println!("  - 169.254.0.0/16 (AWS/GCP/Azure metadata)");
    println!("  - fe80::/10 (IPv6 link-local)");
    println!();

    println!("Current protection:");
    let test_ips = vec![
        ("169.254.169.254", "AWS metadata API"),
        ("169.254.169.253", "Azure metadata API"),
        ("fe80::1", "IPv6 link-local"),
    ];

    for (ip, description) in test_ips {
        let url = format!("http://{}", ip);
        let is_blocked = !validate_url_safe_simulation(&url);
        println!(
            "  {} ({}): {}",
            ip,
            description,
            if is_blocked {
                "BLOCKED ✓"
            } else {
                "ALLOWED ✗"
            }
        );
    }
    println!();

    println!("VULNERABILITY: If DNS rebinds to link-local after validation,");
    println!("metadata API may be accessible despite URL-level protection");
}

/// Demonstrates the fix: DNS response pinning.
///
/// Shows how to prevent DNS rebinding by resolving once and reusing the IP.
#[tokio::test]
#[ignore]
async fn test_dns_rebinding_mitigation_pinning() {
    use hickory_resolver::TokioResolver;
    use std::sync::Arc;

    println!("=== DNS Rebinding Mitigation: Response Pinning ===\n");

    let resolver = Arc::new(
        TokioResolver::builder_tokio()
            .expect("Failed to create resolver builder")
            .build(),
    );

    let domain = "example.com";
    println!("Secure DNS resolution pattern:");
    println!();

    // Step 1: Resolve DNS
    println!("[Step 1] Resolve DNS:");
    let lookup = resolver
        .lookup_ip(domain)
        .await
        .expect("DNS resolution failed");
    let ip = lookup.iter().next().expect("No IP returned");
    println!("  Domain: {}", domain);
    println!("  Resolved IP: {}", ip);
    println!();

    // Step 2: Validate resolved IP
    println!("[Step 2] Validate resolved IP:");
    let is_public = validate_ip_is_public(ip);
    println!("  IP: {}", ip);
    println!("  Is public: {}", is_public);
    println!(
        "  Validation: {}",
        if is_public { "PASS ✓" } else { "FAIL ✗" }
    );
    println!();

    // Step 3: Use IP directly for connection (pinning)
    println!("[Step 3] Connect using pinned IP:");
    println!("  Connect to: {} (not domain)", ip);
    println!("  Host header: {}", domain);
    println!("  Benefit: DNS cannot rebind during connection");
    println!();

    println!("MITIGATION: DNS response pinning prevents rebinding");
    println!("Once IP is validated, use it directly for all requests");
}

/// Simulates URL validation (simplified version of actual validation).
fn validate_url_safe_simulation(url_str: &str) -> bool {
    // Check if URL contains obvious private/localhost strings
    if url_str.contains("127.0.0.1")
        || url_str.contains("localhost")
        || url_str.contains("192.168.")
        || url_str.contains("10.")
    {
        return false;
    }

    // Check scheme
    if !url_str.starts_with("http://") && !url_str.starts_with("https://") {
        return false;
    }

    true
}

/// Validates that an IP address is public (not private/local).
fn validate_ip_is_public(ip: IpAddr) -> bool {
    match ip {
        IpAddr::V4(ipv4) => is_public_ipv4(ipv4),
        IpAddr::V6(_ipv6) => {
            // Simplified: assume IPv6 needs similar checks
            true
        }
    }
}

/// Checks if an IPv4 address is public (not private/reserved).
fn is_public_ipv4(ip: Ipv4Addr) -> bool {
    let octets = ip.octets();

    // Private ranges (RFC 1918)
    if octets[0] == 10 {
        return false; // 10.0.0.0/8
    }
    if octets[0] == 172 && octets[1] >= 16 && octets[1] <= 31 {
        return false; // 172.16.0.0/12
    }
    if octets[0] == 192 && octets[1] == 168 {
        return false; // 192.168.0.0/16
    }

    // Loopback
    if octets[0] == 127 {
        return false; // 127.0.0.0/8
    }

    // Link-local (APIPA)
    if octets[0] == 169 && octets[1] == 254 {
        return false; // 169.254.0.0/16 (AWS/cloud metadata APIs)
    }

    // Broadcast
    if ip == Ipv4Addr::BROADCAST {
        return false;
    }

    // Unspecified
    if ip == Ipv4Addr::UNSPECIFIED {
        return false;
    }

    true
}

/// Documents the attack surface and recommendations.
#[tokio::test]
#[ignore]
async fn test_dns_rebinding_recommendations() {
    println!("=== DNS Rebinding Protection Recommendations ===\n");

    println!("Current vulnerabilities:");
    println!("  1. URL validation checks URL string, not resolved IP");
    println!("  2. DNS resolution happens after validation (TOCTOU gap)");
    println!("  3. No IP validation after DNS resolution");
    println!("  4. HTTP client may re-resolve DNS during connection");
    println!();

    println!("Recommended fixes (Priority order):");
    println!();

    println!("P0 (Critical - SSRF bypass):");
    println!("  1. Resolve DNS during URL validation");
    println!("  2. Validate ALL resolved IPs are public");
    println!("  3. Pin DNS response: use resolved IP for connection");
    println!("  4. Add 'Host' header with original domain for TLS SNI");
    println!();

    println!("P1 (Defense in depth):");
    println!("  5. Reject domains with TTL < 60 seconds");
    println!("  6. Cache DNS responses, don't re-resolve");
    println!("  7. Implement DNS response monitoring (detect rebinding)");
    println!("  8. Rate-limit requests per domain (slow down attacks)");
    println!();

    println!("P2 (Operational):");
    println!("  9. Log DNS resolutions for audit trail");
    println!("  10. Alert on DNS responses with private IPs");
    println!("  11. Document known-safe domains (allowlist)");
    println!("  12. Implement network egress filtering");
    println!();

    println!("Example secure flow:");
    println!("  1. Parse URL: http://example.com");
    println!("  2. Validate URL format and scheme");
    println!("  3. Resolve DNS: example.com → [93.184.216.34]");
    println!("  4. Validate ALL IPs are public");
    println!("  5. If valid: Connect to 93.184.216.34 with Host: example.com");
    println!("  6. Never re-resolve DNS for this request");
    println!();

    println!("Note: Current src/security/url_validation.rs provides URL-level");
    println!("protection but is vulnerable to DNS rebinding attacks");
}
