STP Attack Explained | Simple Guide to Spanning Tree Protocol Vulnerabilities and Prevention (2025)

Table of Contents

•  What Is STP and Why Is It Important?
• Key STP Terms Made Easy
• How STP Attacks Work (2 Simple Ways)
•  Real-Life Example
• How to Protect Your Network from STP Attacks
• How to Detect an STP Attack
•  Modern Alternatives to STP
• Conclusion
•  Frequently Asked Questions (FAQs)

Spanning Tree Protocol (STP) is used in networks to stop loops when there are multiple network paths. But hackers can misuse this system to cause problems or take control of traffic in your network.

In this blog, we’ll explain STP attacks in a very simple way. You’ll learn how attackers use it, real examples, and how to protect your network.

 What Is STP and Why Is It Important?

In computer networks, if there are multiple paths, it can create loops, which confuse switches and slow everything down. To fix that, STP (Spanning Tree Protocol) picks one main path and blocks the rest.

But here’s the problem: STP trusts all devices, so if a hacker tricks it, they can become the “boss” switch (called the Root Bridge) and redirect traffic their way.

Key STP Terms Made Easy

 How STP Attacks Work (2 Simple Ways)

 1. Root Bridge Hijack (Fake Main Switch)

Example:
An attacker connects a laptop to an open office port. Using a tool like Yersinia, they send fake network messages that say:

“Hey, I’m the best switch—make me the boss!”
Since they set a very low Bridge ID, the real switches believe them and send all traffic through the attacker’s laptop. That allows spying or stealing data.

 2. BPDU Flood (Confuse the Network)

The attacker sends too many fake messages (BPDUs), forcing all switches to constantly reset. This causes slow networks, outages, or complete network crashes.

 Real-Life Example

In a security test in 2024, a red team plugged a laptop into a campus network. In less than 30 seconds, they tricked the switches to send all data through their device. They then captured sensitive files, passwords, and emails — without any alert going off!

✅ How to Protect Your Network from STP Attacks

Here’s a checklist to help stop STP attacks — explained simply:

Tip: Always turn on BPDU Guard for user ports and Root Guard for uplinks to other networks.

 How to Detect an STP Attack

• Watch for messages like ROOT_CHANGE in switch logs

• Check for slower speeds or broadcast traffic spikes

• Use your SIEM tool to alert if laptops or phones send BPDUs

If you see something suspicious — disable the port right away and check the device physically.

 Modern Alternatives to STP

STP is still used, but new methods are safer and faster. Here are some:

But remember, even with new tech — you must still protect the edge ports (user connections).

Conclusion

• STP can be tricked if not protected

• Hackers can use fake switch messages to steal data or crash your network

• Turn off trunking, enable BPDU guard, and watch your logs

• Regularly check your switch settings and train your IT staff

Protect your Layer 2 — before it becomes your weakest link.

 FAQs 

What is an STP attack in networking?

An STP attack is when a hacker tricks the Spanning Tree Protocol to change the network’s topology and redirect traffic through a malicious device.

How does the Spanning Tree Protocol work?

STP prevents network loops by selecting one main path (Root Bridge) and blocking others.

Why is STP vulnerable to attacks?

Because STP trusts all switches, attackers can send fake Bridge Protocol Data Units (BPDUs) to hijack the root bridge role.

What is BPDU in STP?

BPDU stands for Bridge Protocol Data Unit. It's a message used by switches to share network topology info.

What is BPDU spoofing?

It’s when a device sends fake BPDUs to manipulate STP and become the root bridge.

What happens if an attacker becomes the root bridge?

They can control or sniff traffic, disrupt services, or cause loops in the network.

What tools are used for STP attacks?

Tools like Yersinia and Ettercap can generate fake BPDUs to launch STP attacks.

Can an attacker crash a network with STP?

Yes, by flooding the network with fake BPDUs, attackers can force constant reconfiguration, leading to network outages.

What is Root Guard in STP?

It prevents other devices from becoming the root bridge by blocking suspicious BPDUs.

What is BPDU Guard?

It shuts down a port immediately if a BPDU is received unexpectedly, protecting user ports.

What is the difference between STP and RSTP?

RSTP (Rapid STP) is a faster version that recovers from changes more quickly but still shares similar risks.

How do I know if my switch is under STP attack?

Look for signs like constant root bridge changes, high CPU usage, or BPDU alerts in logs.

How to stop STP attacks in Cisco switches?

Use bpduguard enable, root guard, and disable trunking on access ports.

What does ‘switchport mode access’ do?

It prevents a port from auto-negotiating trunk mode, which adds a layer of security.

Can STP be disabled?

Yes, but only if your network topology doesn’t require it. In most cases, it’s safer to harden it instead.

What is VLAN hopping in relation to STP?

Though different, both exploit Layer 2 flaws. VLAN hopping targets VLANs, while STP attacks target loop control.

Is STP attack a man-in-the-middle attack?

It can be. If a malicious device becomes the root bridge, it can intercept and modify traffic.

Can Wi-Fi networks be affected by STP attacks?

Indirectly, yes—especially if access points are connected to vulnerable switches.

How do I protect edge ports from STP attacks?

Enable BPDU Guard and disable trunking on ports that connect to user devices.

What is a native VLAN, and how does it relate to STP?

The native VLAN is used for untagged traffic and can be a weak point if not secured alongside STP.

What is a MAC flooding attack?

It’s different from STP attacks but can also cause Layer 2 disruption by overloading the switch.

How often should I audit STP configurations?

At least quarterly, or immediately after network changes.

What is port security, and how does it help against STP attacks?

It limits the number of devices per port, reducing rogue switch risks.

What is DTP and why disable it?

DTP (Dynamic Trunking Protocol) auto-negotiates trunk ports. Disabling it prevents accidental or malicious trunking.

What does “spanning-tree portfast” do?

It speeds up connection for end devices but should be combined with BPDU Guard for safety.

Can STP attacks be detected by firewalls?

Not usually. They happen at Layer 2, which most firewalls don’t monitor.

Is STP used in cloud networks?

Not directly. Cloud data centers use newer methods like VXLAN or TRILL.

What are alternatives to STP?

EVPN, TRILL, SPB, and SDN-based approaches offer better control and security.

Do home routers use STP?

Some do, but it's more relevant in enterprise and campus networks.

What should I include in an STP hardening checklist?

BPDU guard, Root Guard, port security, disabled trunking, STP alerts, and regular audits.