When it comes to cyber security, most businesses have heard of man-in-the-middle attacks. But fewer are familiar with the quieter and arguably sneakier threat – the man-on-the-side attack (MotS). While it’s less well known, it can be just as damaging, particularly if your network security isn’t up to scratch.

What is a Man-on-the-side Attack?

A man-on-the-side-attack is a type of cyber attack where the attacker monitors a network and waits for an opportunity to inject malicious content into a data stream. Unlike a man-in-the-middle attack, where the attacker can intercept and alter communications between two parties, a MotS attacker can only observe and inject, they can’t stop or modify the original traffic.

How Do Man-on-the-Side Attacks Work?

MotS attacks rely on weak or unencrypted network traffic. They typically target:

• Unsecured web traffic (e.g. websites using HTTP instead of HTTPS)
• Unencrypted DNS requests
• Open Wi-Fi networks or poorly configured corporate networks

Here’s a simplified example 👉 A user on your company’s network tried to visit a genuine website. The attacker, watching the network, sees the request and quickly fires back a fake response. If their response arrives before the legitimate one, the user could be redirected to a convincing fake website, where they might unknowingly enter sensitive information.

These attacks can be particularly effective when combined with phishing tactics or malware injection. In some high-profile cases, even government-level surveillance tools have used man-on-the-side techniques to intercept and manipulate data in transit.

Why Should Businesses Be Concerned?

It’s a common misconception that cyber criminals only go after big corporations. In reality, small and medium-sized businesses are often targeted because they may have weaker network security in place.

A successful man-on-the-side attack can lead to:

• Sensitive data theft – including login credentials, financial information or client data
• Malware infections – injected through fake websites or downloads
• Financial loss – due to fraud or costly system recovery
• Reputational damage – particularly if customer data is exposed

These attacks often happen silently, without immediate signs of intrusion. By the time the issue is spotted, the damage has already been done.

How to Protect Your Business Against Man-on-the-Side Attacks

Fortunately, there are practical steps businesses can take to reduce the risk of a man-on-the-side attack.

Prioritise Encryption

Make sure your network traffic is encrypted wherever possible. Websites should use HTTPS, and employees should avoid using unsecure Wi-Fi networks. Virtual Private Networks (VPNs) can also help protect data by encrypting traffic between devices and servers.

Use DNS Over HTTPS (DoH)

Traditional DNS lookups are often sent in plain text, making them easy for attackers to see and exploit. Switching to DNS over HTTPS ensures these requests are encrypted, preventing attackers from intercepting or manipulating them.

Adopt a Zero Trust Security Approach

The zero trust model assumes that no device or user is inherently trustworthy – even those already inside your network. Zero trust security involves verifying every access attempt, using principles like least privilege, multi-factor authentication, and network segmentation.

Monitor and Detect Suspicious Traffic

Having robust monitoring tools in place can help identify unusual network activity (like unexpected DNS requests or duplicate responses to a web request), which could signal a man-on-the-side attack. Managed IT services can offer ongoing network monitoring and intrusion detection to catch threats early.

Stay Ahead of Cyber Threats

While the MotS attack might not be as well known as other cyber threats, it’s no less dangerous. Its ability to quietly intercept and manipulate network traffic can lead to serious consequences for businesses of all sizes.

As cyber attacks become more sophisticated, relying on traditional defences simply isn’t enough. Encryption, strong network security practices, and a zero trust approach are essential tools in reducing your exposure to this type of attack.

If you’re unsure whether your business is protected against these threats, it might be time to have a conversation. Our team specialises in helping businesses strengthen their cyber defences with practical, cost-effective solutions tailored to your needs.

After all, when it comes to cyber security, it’s always better to be safe than compromised.