3. Load Balancer Security- Defending Against Attacks

Bypassing Load Balancers: Techniques & Methods

Load balancers act as traffic distributors, ensuring high availability and security. However, attackers can bypass load balancers using misconfigurations, direct server access, or evasion techniques.

1. Direct IP Access (Origin Server Exposure)

🔥 Attack Method

• Many websites have an origin server (actual backend server) that sits behind a load balancer.

🛠 How Attackers Find Origin Servers:

🔒 Mitigation

✅ Use Cloudflare / AWS Route 53 DNS masking
✅ Restrict direct access to the origin server (allow only LB IPs)
✅ Configure firewall rules to allow traffic only from the load balancer

2. Host Header Injection (Server-Side Confusion)

🔥 Attack Method

• Some backend servers trust the Host header to determine which domain to serve.
• If the load balancer forwards the request without validation, an attacker can manipulate the header to access internal apps.

🛠 Exploit Example

GET /admin HTTP/1.1
Host: internal.target.com

🔒 Mitigation

✅ Enable Strict Host Header Validation
✅ Use WAF rules to block unexpected Host headers

3. X-Forwarded-For (XFF) Header Abuse

🔥 Attack Method

• Many load balancers forward the client’s IP using the X-Forwarded-For header.
• Attackers can spoof this header to evade rate limits and WAF rules.

🛠 Exploit Example

X-Forwarded-For: 127.0.0.1

🔒 Mitigation

✅ Use rate limiting based on session tokens instead of IP
✅ Configure WAF to verify only trusted proxies

4. Slow HTTP Attacks (Slowloris Bypass)

🔥 Attack Method

• Slowloris Attack keeps connections open without completing requests, exhausting server resources.
• Some Layer 7 Load Balancers fail to detect this if request timeouts aren’t enforced.

🛠 Exploit Example

slowhttptest -c 1000 -H -g -o output -u http://target.com -r 200 -l 300

🔒 Mitigation

✅ Set aggressive timeout policies on incomplete HTTP headers
✅ Block clients with high connection persistence

5. WebSocket Load Balancer Bypass

🔥 Attack Method

• Many load balancers don’t inspect WebSocket traffic (ws://), allowing attackers to tunnel malicious payloads.

🛠 Exploit Example

var ws = new WebSocket("ws://target.com/admin");
ws.send("GET /bypass-admin HTTP/1.1");

🔒 Mitigation

✅ Use Layer 7 WAF with WebSocket inspection
✅ Restrict unauthenticated WebSocket connections

6. API Rate Limiting Bypass

🔥 Attack Method

• Rotate IPs using botnets to bypass API rate limits.
• Use different tokens (JWT, OAuth) to bypass per-user restrictions.

🛠 Exploit Example

for i in {1..1000}; do curl -H "Authorization: Bearer token_$i" http://api.target.com/login; done

🔒 Mitigation

✅ Use behavior-based rate limiting (not just IP-based)
✅ Implement reCAPTCHA for sensitive API endpoints

7. Load Balancer Cache Poisoning

🔥 Attack Method

• If the load balancer caches user input, an attacker can inject malicious responses into the cache.
• This leads to stored XSS, CSRF, or HTML Injection.

🛠 Exploit Example

GET /search?q=<script>alert(1)</script> HTTP/1.1

🔒 Mitigation

✅ Disable caching for dynamic pages
✅ Sanitize user input before caching

8. Bursting Traffic to Overload Load Balancer

🔥 Attack Method

• Instead of a sustained DDoS, attackers send bursts of high-volume traffic to exhaust rate limits and WAF rules.

🛠 Exploit Example

hping3 -c 5000 -d 120 -S -w 64 -p 443 --flood target.com

🔒 Mitigation

✅ Use behavior-based traffic analysis (AI-based WAFs)
✅ Enable auto-scaling to absorb spikes

💡 Final Thoughts

🔹 Load balancers help mitigate attacks, but attackers can still find ways to bypass them.
🔹 Combining WAF, rate limiting, strict origin access, and anomaly detection is key.

Would you like a hands-on demo of any technique? 🚀

A. Introduction to Load Balancers

A Load Balancer distributes incoming traffic across multiple backend servers to ensure high availability, fault tolerance, and optimal resource utilization. It operates at Layer 4 (Transport Layer) and Layer 7 (Application Layer), helping to mitigate failures, balance workloads, and provide security enhancements like Web Application Firewall (WAF), Rate Limiting, and DDoS Protection.

graph TD
    User[User Requests] -->|Traffic Distribution| LB[Load Balancer]
    LB -->|Balanced Request| Server1[App Server 1]
    LB -->|Balanced Request| Server2[App Server 2]
    LB -->|Balanced Request| Server3[App Server 3]

B. Load Balancer Security Tools & Defenses

C. Load Balancer Attack Detection & Prevention Tools