Imagine that someone has cloned your identity. Now this person goes to banks, stores and various establishments, asking for answers and services in your name. These places, trusting that you are who you say you are, respond promptly. There’s just one problem: you never made these requests, but now you’re being bombarded with all the answers.
This is how a SYN-ACK Reflection attack works, one of the most complex and devastating threats in the digital world. But what makes it really dangerous is not the volume of traffic itself – but the fact that it comes from legitimate servers.
At Huge Networks, we face attacks like this frequently. And we’ve discovered that the biggest problem isn’t just filtering packets – it’s understanding that the servers that are attacking us aren’t to blame at all. They’ve been tricked, just like the victim.
Chaos Engineering: How the attacker uses legitimate servers against you
Unlike conventional DDoS attacks, where the attacker controls botnets to generate traffic directly to the victim, in SYN-ACK Reflection, he doesn’t even need his own servers.
It uses a technique called IP Spoofing, where it falsifies the source IP of the packets. With this, it sends millions of SYN packets to legitimate servers – only instead of using its own IP as the sender, it uses the victim’s IP.
What happens next? The servers respond with SYN-ACK packets, believing that they are communicating with a real client. The result is that the target receives a massive volume of SYN-ACK responses, without ever having made the original request.
Why is this so difficult to mitigate?
- The packages come from legitimate servers, such as cloud providers, banks, large websites and critical infrastructures.
- There is no fixed attack pattern – source IPs change constantly, as any server on the Internet can be used as a “weapon”.
- Traffic often goes unnoticed by traditional filters because it appears to be a response to a legitimate connection.
In practice, the internet itself is attacking the victim, without the servers involved knowing it.
Why do 90% of companies fail to mitigate this attack?
Most DDoS mitigation solutions rely on connection state analysis, ratelimits or TCP header pattern analysis. The problem? In the case of SYN-ACK Reflection, we don’t see the start of the communication – only the responses.
If we had access to the client’s upload traffic, we could validate whether it really sent the SYNs. But in most cases, this isn’t possible.
This means
- Traditional solutions fail because they try to block source IPs without realizing that the blocked servers are legitimate.
- The traffic can go unnoticed by firewalls, as it appears to be a legitimate response to non-existent connections.
- The attack can saturate entire networks before it is even detected, since the problem manifests itself in PPS (packets per second), not just bandwidth.
In other words, 90% of companies simply can’t deal with this type of attack, because it exploits vulnerabilities in the very architecture of the internet.
The mitigation game: How we survive chaos
Facing a SYN-ACK Reflection attack requires advanced network engineering and techniques that go far beyond simple packet filtering. At Huge Networks, we have adopted strategies that ensure our customers are protected, even under the biggest digital storm they have ever seen.
1. intelligent identification of anomalous traffic
- We create statistical patterns to detect anomalies in SYN-ACK traffic.
- If a legitimate server sends SYN-ACK responses without having received real SYNs, it is classified as a victim of spoofing and treated in a special way.
2. TCP SYN Proxy – Filtering False Connections
- We have implemented a similar approach to SYN Proxy, where we force a TCP pseudo-handshake to ensure that only real connections are forwarded.
- If a SYN-ACK arrives without a corresponding SYN in our base, we discard the packet.
3. Intelligent Ratelimiting and Bloom Filters
- Bloom Filters help track down IPs that have not completed the handshake and temporarily block this traffic.
- We apply dynamic rate limiting, adjusting the limits automatically as the attack evolves.
4. Traffic Engineering and Network Balancing
- SMP balancing optimization to avoid bottlenecks in routers and switches.
- Load distribution between multiple scrubbing centers, ensuring that a single point is not overloaded.
5. Global Monitoring of Reflection Servers
- We have created a dynamic list of the most used servers for reflection, applying temporary filters to reduce the impact of attacks.
- We maintain relationships with ISPs and operators to alert them to servers being misused.
The challenges beyond mitigation: When infrastructure fails
Even with all these techniques, attacks of this magnitude expose weaknesses that go beyond direct mitigation. We have already faced cases where Tier 1 operators themselves collapsed before the traffic reached us. Furthermore, even modern hardware presents severe limitations in the face of an attack on this scale.
1. Tier 1 operators saturated
- In extreme attacks, SYN-ACK traffic can congest global backbones before it even reaches our infrastructure.
- Some operators simply start dropping packets, resulting in outages before mitigation kicks in.
2. Modern Hardware Limitations
- The PCI Express (PCIe) bus becomes an unexpected bottleneck because the packet rate (PPS) exceeds the system’s ability to move data from the NIC to the CPU.
- Solutions to mitigate this include:
- NICs optimized for high PPS (such as Mellanox ConnectX and Intel E810).
- IRQ adjustment and packet coalescing to avoid system overload.
Conclusion: We are dealing with a new era of DDoS
Digital warfare is evolving. Attacks like SYN-ACK Reflection aren’t just volumetric – they’re ingenious. They use the internet’s own infrastructure against itself, exploiting spoofing, traffic balancing and hardware limitations to create a perfect storm.
While most operators can’t cope with this attack pattern, we learn, adapt and evolve.
What sets us apart is not just the technology – it’s the way we think about the problem. We know that mitigation starts before the attack is even detected, and our approach ensures that our clients are protected while the rest of the internet collapses.
There is no end to the digital war.
But for now, we’re winning.
Welcome to Huge Networks. Here, we turn chaos into control.
Thanks for reading!
What's your reaction?
