Robert Derby
Senior Security Product Marketing Manager
Understanding MiTM Attacks
You send information to someone you trust. They send information back.
But what if someone else is secretly sitting between you?
That is the basic idea behind a man-in-the-middle (MitM) attack.
An attacker gets between two people, systems, or services that believe they are communicating directly. From that position, the attacker may be able to watch the communication, steal information, redirect traffic, or even change what is being sent.
The dangerous part is that everything may still appear normal.
You may also hear the term adversary-in-the-middle (AiTM). It describes the same basic concept and is the terminology used by MITRE ATT&CK.
How does a man-in-the-middle attack work?
Most MitM attacks follow a simple pattern.
- The attacker gets into the communication path
First, the attacker finds a way to place themselves between two parties.
That could mean tricking a device into sending traffic to the wrong destination, creating a fraudulent Wi-Fi network, redirecting network traffic, or placing an attacker-controlled website between a user and a legitimate service.
Each technique works differently, but all redirect communication through attacker-controlled infrastructure.
- Everything still looks legitimate
A successful MitM attack aims to avoid disrupting communication.
The user may still reach the website they expected. The application may continue working. The other system may still receive the information.
That apparent normalcy is what makes the attack dangerous.
The attacker is in the middle, but neither side necessarily knows it.
- The attacker uses that position
Depending on the attack, the adversary may be able to:
- Steal usernames, passwords, or other sensitive information
- Capture authentication or session information
- Redirect users to malicious destinations
- Monitor network communications
- Change information as it travels between systems
- Gather intelligence for a larger attack
A MitM attack is therefore more than simple eavesdropping. The attacker may be able to influence the communication itself.
What are common types of man-in-the-middle attacks?
There is no single MitM technique. Attackers can get into the middle in several ways.
Rogue or “evil twin” Wi-Fi
An attacker creates a wireless network that looks legitimate. A user connects to it, allowing network traffic to pass through the attacker-controlled infrastructure.
Network traffic redirection
Attackers can manipulate network services that devices rely on to find other systems. Techniques such as ARP poisoning, DNS manipulation, or DHCP spoofing can redirect communications toward an attacker-controlled system.
The terminology can sound complicated, but the principle is simple: convince the device to send traffic somewhere it should not go.
Website and authentication interception
Modern attacks can also place a malicious website between a user and a legitimate online service.
The victim may believe they are signing into the real service. The attacker passes the information along, while potentially capturing credentials or the authenticated session.
This is often called an adversary-in-the-middle phishing attack.
Encryption and certificate attacks
Attackers may also try to exploit weaknesses in how encrypted connections are configured or trusted.
That is why encryption alone is not enough. Systems also need to verify that they are communicating with the correct destination.
Doesn't HTTPS prevent MitM attacks?
HTTPS makes man-in-the-middle attacks much harder, but there is an important distinction.
- Encryption protects the contents of communication.
- Authentication helps prove who is on the other end.
Modern Transport Layer Security (TLS), which powers HTTPS, is designed to provide both. Proper certificate validation helps a browser or application verify that it reached the intended service rather than an impostor.
That is why browser certificate warnings matter. When you see a browser certificate warning, it indicates that either encryption or authentication is at risk.
But HTTPS does not eliminate every possible intermediary attack. Problems can still arise from weak configurations, compromised trust, user behavior, malicious proxies, or attacks aimed at authentication sessions rather than the encrypted connection itself.
HTTPS remains an important defense because secure communication depends on both encryption and verifying who is on the other end.
How can organizations reduce the risk of MiTM Attacks?
There is no single MitM security control. Organizations reduce risk by making it harder for an attacker to enter the communication path and harder to impersonate a trusted system.
Important practices include:
- Use current encryption protocols and secure configurations
- Properly manage and validate digital certificates
- Protect DNS, wireless networks, routing, and other network infrastructure
- Avoid bypassing unexpected certificate warnings
- Use phishing-resistant authentication where appropriate
- Segment networks to limit how far an attacker can move
- Monitor for unexpected network communications and configuration changes
Users also play a role. Connecting to unknown wireless networks, ignoring certificate warnings, or entering credentials after following suspicious links can create opportunities for interception.
How do you detect a man-in-the-middle attack?
This is where MitM attacks become challenging.
There is no single alert that always means “someone is in the middle.”
Security teams often have to look for changes in how systems are communicating.
That might include:
- A device suddenly communicating through an unexpected destination
- Unusual DNS or network behavior
- Unexpected certificate changes
- Weak or outdated encryption being used
- New wireless access points
- Communications between systems that do not normally interact
- Suspicious activity immediately before or after a login
One event may not prove an attack.
The surrounding network activity often tells the fuller story.
Why network visibility matters when investigating MitM activity
Many security tools can identify pieces of a suspicious event.
An identity system might show that someone logged in. An endpoint tool might detect unusual activity. A firewall might record a connection.
But investigators may still need to answer:
- Who communicated with whom?
- Where did the traffic actually go?
- What happened before and after the suspicious event?
That is where network evidence becomes valuable to threat investigation.
Seeing how systems actually communicated can help analysts determine whether an event was isolated, whether other systems were involved, and how the activity unfolded.
How NETSCOUT helps investigate suspicious network activity
NETSCOUT Omnis Cyber Intelligence analyzes network traffic using CyberStream and vCyberStream sensors deployed across the network.
Instead of relying only on an alert, analysts can examine network communications and historical evidence to understand what happened around suspicious activity.
For a potential MitM incident, this can help analysts investigate which systems communicated, where traffic traveled, whether unexpected communications occurred, and what happened before and after the original security event.
Omnis Cyber Intelligence also provides visibility into areas relevant to this type of investigation, including internal east-west communications, unexpected network behavior, encrypted traffic characteristics, certificate information, and weak encryption configurations.