Rogue DHCP Servers: When the Network Trusts the Wrong Authority

Vesna Ergarac
Jan 16
2 min read

If DNS cache poisoning is like being sent to the right street but the wrong house, then a rogue DHCP server is far worse; it’s a fake authority handing out fake instructions that everyone blindly follows. And that’s exactly why it’s dangerous.

When combined with DNS Cache poisoning, a rogue DHCP server can assign a malicious DNS server which then performs DNS cache poisoning, thus sending users to attacker-controlled destinations. This is why the combination of rouge DHCP servers and DNS Cache poisoning is so deadly.

Its different layers working on the same outcome, with one attack feeding the next.

This is how professional attackers operate - not in isolation, but in chains.

🧠 So, what IS a Rogue DHCP Server?

A rogue DHCP server is an unauthorized device introduced into a network that responds to DHCP requests faster than the legitimate server.

When a client asks: “Can someone give me an IP address?”, the rogue server answers first, and the client accepts its instructions without question. Those instructions can include:

A malicious default gateway
A malicious DNS server
Incorrect network routing
Redirected traffic paths

At that point, the attacker isn’t just on the network, they’re essentially in control of it, directing it as they deem fit.

💥The Real-World Impact

Once a rogue DHCP server is in control, the attacker can Intercept traffic (Man-in-the-Middle attacks), redirect users to malicious websites, collect credentials, monitor internal communications amongst other things. From the user’s perspective, nothing looks wrong, but from the organisation’s perspective, trust has already been lost.

⚠️Why Businesses Should Care

Rogue DHCP attacks are particularly effective in:

Flat networks
Poorly segmented environments
Guest Wi-Fi setups
Legacy infrastructure
Environments without Zero Trust controls

They bypass perimeter security because they don’t attack the perimeter - they abuse internal trust. And trust, once misplaced, is very hard to recover.

🛡️How to Defend Against Rogue DHCP Attacks

Mitigation is not complicated — but it does require intent. Effective controls include:

DHCP snooping on switches
Network segmentation
Port security
Monitoring for unauthorised DHCP responses
Strong internal governance, not just perimeter firewalls

This isn’t about buying more tools. It’s about understanding how networks actually behave.

🎯Final Thoughts from ST3MTech

Rogue DHCP servers aren’t new. What’s changed is how often they go unnoticed. When a network trusts the wrong authority, attackers don’t need exploits - they just need patience. Understanding these attacks isn’t paranoia. It’s literacy. And in cybersecurity, literacy is defence.

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