What Is a Man-in-the-Middle (MITM) Attack? Eavesdropping Cyberattacks

Man-in-the-middle (MITM) attacks are a type of cyberattack where a criminal intercepts data or conversations between two parties (like a user and an application or a client and a server). They can alter or steal the data, or impersonate one of the parties to convince the other they are having an authentic interaction.

Using the MITM attack, criminals can access login credentials, payment information, and other sensitive data. It’s a common entry point for many costly cyberattacks.

These attacks are especially effective in environments where security standards like encryption and authentication aren’t present.

Learn how man-in-the-middle attacks work, examples of common attacks, and how to detect and prevent them.

How Does a Man-In-the-Middle Attack Work?

MITM attacks can happen in multiple ways, but the common denominator is a criminal intercepting some form of communication, rerouting the data to the attacker's desired destination, and then decrypting if necessary. These attacks often happen when a user is attempting to log in to a website or service.

But before we dive into the process, let's review where man-in-the-middle attacks can happen:

Public networks: Password-free WiFi networks are easy to use, but it also makes them an ideal place for a criminal to infiltrate and initiate a MITM attack.
Router: Routers which are set to default passwords or not updated are vulnerable to getting hacked.
Web server: Criminals may hijack servers and reroute traffic to a copycat website.
Phishing email: Criminals often use social engineering phishing emails to trick a person to install malware or hand over their sensitive information.

An attacker will need to get in between the user and the application they are trying to access to successfully become the proxy. They point a gateway's IP address to their MAC address, so when a user makes a request, it's sent to the attacker instead of the gateway, routing all traffic through a proxy.

There are a few different methods for conducting a MITM attack:

Address Resolution Protocol (ARP) spoofing: Also known as ARP cache poisoning, this method tricks a computer into thinking the attacker's computer is the network gateway. The attacker accomplishes this by sending false information to the network to redirect connections.
Domain Name Server (DNS) spoofing: Criminals can divert traffic from a legitimate site to a fake version by altering IP addresses in a DNS server. It can affect a large number of people because it involves hijacking a DNS server and altering records. When someone enters a legitimate website into their browser, the DNS server redirects them to a malicious copycat website. Then the fake website installs malware or steals credentials.
HTTPS spoofing: Criminals obtain a spoofed domain name using non-ASCII characters that looks similar in appearance to a legitimate website. Then the criminals will register an SSL certificate to make the site look authentic. The spoofed website gets sent to people in phishing scams.
Email hijacking: Criminals compromise an email account using phishing scams and then commit other cyberattacks. One example is business email compromise (BEC) which utilizes social engineering and vendor impersonation to exploit trusted relationships.
Man-in-the-browser: This method involves installing malware onto a person's device. This malware records login credentials the user enters on websites. There are multiple ways to trick people into installing malware, but criminals can also accomplish this by finding browser vulnerabilities.
WiFi eavesdropping: Public WiFi networks are vulnerable to a method called eavesdropping. Criminals can compromise the network and monitor user activity including login credentials and payment information. Alternatively, criminals may create a legitimate-appearing public WiFi network to trick users into connecting.
SSL hijacking: This method involves the criminal tricking the user and the application into thinking a session is secure when it's not a secure connection. The cyberattack is executed by forging SSL/TLS certificates between the two parties.
SSL stripping: SSL stripping occurs when a criminal manages to successfully convince a browser to connect to an unencrypted version of a website (HTTP) instead of the encrypted site (HTTPS). This could expose sensitive information to the attacker.

MITM attacks range from highly technical methods to taking advantage of human behavior through social engineering. Organizations should prepare for all of these possible attacks by implementing a multi-layered security approach including technical safeguards and social engineering prevention.

How To Check for a Man-in-the-middle Attack

MITM attacks are hard to detect since they often rely on exploiting real-time data transfers and conversations. However, there are a few signs which indicate a MITM attack when browsing the web.

Severe latency when loading sites or using applications.
A spoofed URL–web5ite.com instead of website.com, for example.
Frequent and random disconnections.
No "S" in the "HTTPS" connection in the web browser.

People should always take caution when using public or unsecured WiFi networks. Criminals can create or hijack these networks with the express intent of committing a man-in-the-middle attack. Once a person connects to a compromised network, a criminal can monitor everything sent over the network.

How To Prevent Man-in-the-Middle Attacks

Prevention is always essential to prevent a cyberattack from infiltrating your network or system. A multi-layered approach to security will give an organization a better defense system against cybercrimes like MITM attacks.

Fortunately, there are many tactics and tools to build a robust cybersecurity system. Some general tips include: