Dns Cache Poisoning in Echo Go

DNS cache poisoning in Echo Go applications typically occurs when user-controlled DNS lookups are performed without proper validation or when cached DNS responses are reused without considering their freshness. Echo Go's HTTP client and DNS resolution mechanisms can be vulnerable to this attack if not properly configured.

The most common manifestation happens through Echo Go's net/http client when making outbound requests to user-provided domains. An attacker can manipulate DNS responses to redirect traffic to malicious servers, potentially leading to data exfiltration, credential theft, or supply chain attacks.

Consider this vulnerable Echo Go pattern:

func handleRequest(c echo.Context) error {
    target := c.QueryParam("api_url")
    
    // Vulnerable: No DNS validation or timeout configuration
    client := &http.Client{
        Timeout: 10 * time.Second,
    }
    
    resp, err := client.Get(target)
    if err != nil {
        return c.String(http.StatusInternalServerError, err.Error())
    }
    defer resp.Body.Close()
    
    return c.String(http.StatusOK, "Response received")
}

This code is vulnerable because it accepts any domain from the query parameter and performs a DNS lookup without validation. An attacker can poison the DNS cache to return malicious IP addresses for legitimate domains, causing Echo Go to connect to attacker-controlled servers.

Another Echo Go-specific scenario involves middleware that performs DNS resolution for rate limiting or authentication:

func rateLimitMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        clientIP := c.RealIP()
        
        // Vulnerable: DNS lookup without validation
        host, err := net.LookupAddr(clientIP)
        if err != nil {
            return next(c)
        }
        
        // Use hostname for rate limiting decisions
        key := fmt.Sprintf("rate:%s", host)
        
        return next(c)
    }
}

This middleware is problematic because it trusts DNS responses for rate limiting decisions, which could be manipulated by an attacker controlling the DNS infrastructure.

Detecting DNS cache poisoning in Echo Go applications requires both static code analysis and runtime monitoring. middleBrick's black-box scanning approach can identify Echo Go-specific DNS vulnerabilities by examining how the application handles external requests and DNS resolution.

For Echo Go applications, middleBrick scans for:

• Unvalidated user input used in DNS lookups or HTTP requests
• Missing DNSSEC validation for critical domain resolutions
• Long DNS cache TTL values that increase poisoning window
• Lack of DNS response validation against expected IP ranges
• Absence of DNS over HTTPS (DoH) or DNS over TLS (DoT) for sensitive resolutions
• Middleware that trusts DNS responses for security decisions
• Hardcoded DNS servers without validation

middleBrick's CLI tool can be integrated into Echo Go development workflows:

npm install -g middlebrick
middlebrick scan https://yourechoapp.com/api/v1/users --output json

The scanner will test for DNS-related vulnerabilities by attempting to resolve domains through the Echo Go application and checking for proper validation mechanisms. It specifically looks for Echo Go patterns like:

// Vulnerable pattern detected
client := &http.Client{
    Timeout: 10 * time.Second,
    // Missing: Transport with custom DNS resolver
}

middleBrick also analyzes Echo Go's middleware chain to identify where DNS responses are used for authentication or authorization decisions, which is a critical security anti-pattern.

Remediating DNS cache poisoning in Echo Go requires a multi-layered approach using Echo Go's native features and Go's networking capabilities. Here are Echo Go-specific fixes:

First, implement DNS validation using custom HTTP transports:

type validatedTransport struct {
    http.RoundTripper
    allowedIPs map[string]bool
}

func (v *validatedTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    host, _, err := net.SplitHostPort(req.URL.Host)
    if err != nil {
        host = req.URL.Host
    }
    
    // Validate against expected IP ranges
    addrs, err := net.LookupIP(host)
    if err != nil {
        return nil, fmt.Errorf("dns resolution failed: %w", err)
    }
    
    for _, ip := range addrs {
        if v.allowedIPs[ip.String()] {
            // Create new request with validated IP
            req.URL.Host = ip.String()
            return v.RoundTripper.RoundTrip(req)
        }
    }
    
    return nil, fmt.Errorf("resolved IP not in allowed range")
}

func secureClient(allowedIPs map[string]bool) *http.Client {
    return &http.Client{
        Timeout: 10 * time.Second,
        Transport: &validatedTransport{
            RoundTripper: http.DefaultTransport,
            allowedIPs: allowedIPs,
        },
    }
}

// Echo Go handler
func handleRequest(c echo.Context) error {
    target := c.QueryParam("api_url")
    
    // Define allowed IP ranges for your service
    allowed := map[string]bool{
        "192.168.1.1": true, // Example: your API server
    }
    
    client := secureClient(allowed)
    resp, err := client.Get(target)
    if err != nil {
        return c.String(http.StatusInternalServerError, err.Error())
    }
    defer resp.Body.Close()
    
    return c.String(http.StatusOK, "Response received")
}

For Echo Go middleware, implement DNS response validation:

func secureRateLimitMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        clientIP := c.RealIP()
        
        // Use DNS over HTTPS for secure resolution
        resolver := &net.Resolver{
            PreferGo: true,
            Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
                // Use Cloudflare DoH
                return net.Dial("udp", "1.1.1.1:443")
            },
        }
        
        // Validate DNS response against expected ranges
        addrs, err := resolver.LookupIP(c.Request().Context(), "ip", clientIP)
        if err != nil || len(addrs) == 0 {
            return c.String(http.StatusForbidden, "DNS validation failed")
        }
        
        // Only allow private network ranges
        if !isPrivateIP(addrs[0]) {
            return c.String(http.StatusForbidden, "Invalid client IP range")
        }
        
        return next(c)
    }
}

func isPrivateIP(ip net.IP) bool {
    return ip.IsPrivate() || ip.IsLoopback() || ip.IsLinkLocalUnicast()
}

Echo Go's context-based request handling allows for per-request DNS validation:

func dnsAwareHandler(c echo.Context) error {
    ctx := c.Request().Context()
    
    // Validate target domain before use
    target := c.QueryParam("endpoint")
    if !isValidDomain(target) {
        return c.String(http.StatusBadRequest, "Invalid domain")
    }
    
    // Use context with timeout for DNS operations
    ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
    defer cancel()
    
    // Perform validated DNS lookup
    addrs, err := net.DefaultResolver.LookupIP(ctx, "ip", target)
    if err != nil || len(addrs) == 0 {
        return c.String(http.StatusBadGateway, "DNS resolution failed")
    }
    
    // Store validated IPs in context for downstream use
    c.Set("validated_ips", addrs)
    
    return next(c)
}

These Echo Go-specific patterns ensure that DNS responses are validated before being trusted, significantly reducing the risk of cache poisoning attacks.