Man-in-the-Middle (MITM) Attack: How to Recognize and Defend Against One of the Most Insidious Cyberattacks

Have you ever received an invoice via email and noticed that something didn’t add up —perhaps an IBAN code that was different from usual, unusual language in the body of the message, or an unusually urgent request for payment? In an increasingly risky digital environment, even a seemingly insignificant detail can be a sign of a cyber fraud attempt, such as in the case of man-in-the-middle attacks.

Today we’ll take a look at what MITM attacks are, how they work, what the risks are, and—most importantly—how you can protect yourself and your company.

Table of Contents

What is a man-in-the-middle (MITM) attack?

A man-in-the-middle (MITM) attack is a technique used by hackers to intercept communication between two parties —such as a customer and a supplier— without either of them realizing it. The goal? To steal confidential information, tamper with transmitted data, or divert payments to fraudulent bank accounts.

A company that has not implemented measures to protect against a cyberattack.

What does a Man-in-the-Middle attacker look for?

A man-in-the-middle attack has a specific goal: to infiltrate a digital communication between two trusting parties, with the intent to observe, record, manipulate, or exploit the exchanged data without the victims’ knowledge. This type of attack exploits the implicit trust between sender and recipient—whether it be an email conversation, a connection to a website, or a financial transaction—to gain an illicit advantage.

Theft of login credentials

The attacker intercepts usernames and passwords, temporary tokens, PINs, or two-factor authentication codes. This information allows the attacker to access:

Personal or work email addresses
Bank accounts or business accounts
Healthcare, tax, or administrative portals

Once they have gained access, the attacker can act undisturbed, impersonating the legitimate user and exponentially increasing the risk of subsequent fraud.

Interception of financial data

Among the most common targets are bank and payment details:

Credit or debit card numbers
IBAN codes
Outgoing transfer details
Information contained in invoices

This data can be resold on the dark web, used for direct fraud, or to deceive other parties.

Manipulation of communications

In some MITM attacks, the goal is not just to eavesdrop, but to alter the content of communications in real time. This may include:

Editing an invoice with fraudulent bank details
Including malicious links in a legitimate email
Alteration of messages or operating instructions

The victim receives a message that appears to be genuine but has actually been tampered with to benefit the attacker.

Collection of personal or strategic data

The information collected is not only used for immediate scams, but also to build detailed profiles for use in subsequent attacks:

Customer Information
Confidential reports, business strategies, or health data
Legal or contractual information

The goal is to gain an unfair competitive advantage (e.g., industrial espionage) or to blackmail the victims.

Distribution of malware or ransomware

In some cases, MITM is used as a means of injecting malicious code into communications or transmitted files:

Malware that records every keystroke (keylogger)
Ransomware that encrypts data and demands a ransom
Trojans that grant permanent access to the device

Often, all of this happens without the user noticing any visible changes in communication.

In summary: a man-in-the-middle attacker is not only interested in the data itself, but also in the power to access, control, and manipulate that comes from infiltrating the digital trust between two parties. It is precisely this ability to operate silently, without any apparent disruption, that makes it one of the most dangerous and insidious attacks in the field of cybersecurity.

How a MITM attack works

A man-in-the-middle (MITM) attack relies on a strategy that is as simple as it is insidious: sneaking in between two parties who are communicating online, either by impersonating one of them or simply by intercepting the data flowing between them.

On the surface, everything seems to be working normally: emails arrive, websites load, and transactions go through successfully. In reality, however, the attacker is monitoring, copying, or altering the data being transmitted, often without leaving any immediate trace.

The two key stages of a man-in-the-middle attack

A man-in-the-middle attack generally unfolds in two phases: interception and manipulation or monitoring.

1. Interception of communications

This is the moment when the attacker “intervenes” in the digital conversation between two parties. This can be done using various techniques, depending on the environment (public or corporate) and the security level of the networks involved.

The most common techniques include:

Accessing public or unsecured Wi-Fi networks
Hackers can create fake Wi-Fi hotspots with misleading names (e.g., “Hotel_Free_WiFi”), tricking users into connecting. All transmitted data—logins, emails, credit card numbers—is then intercepted in plain text.
ARP Spoofing (Address Resolution Protocol)
Within a local network, an attacker sends forged messages to the router, pretending to be another device. This allows the attacker to redirect traffic to their own computer.
DNS (Domain Name System) Spoofing
The attacker manipulates the system that translates web addresses into IP addresses, redirecting the user to counterfeit sites that look identical to the real ones.
Session Hijacking
If the user is already authenticated (e.g., on a bank account), the attacker intercepts the session token, thereby stealing the user’s identity and taking control of the current session.

The goal of this first phase is to take control of the communication channel or redirect the data to a channel controlled by the attacker.

2. Data manipulation or monitoring

Once the attacker gains access to the data stream, they can either simply listen in (passive attack) or actively intervene to modify or exploit the information.

Reading of confidential data
Emails, chat messages, login credentials, attached documents, and sensitive data are viewed, recorded, and sometimes stored for future attacks.
Content Modification A classic example is the replacement of the IBAN in a PDF invoice attached to an email. The recipient pays in good faith, but the money ends up in the attacker’s account.
Redirection to fake websites (pharming)
The user enters a valid URL but is redirected to a malicious copy of the website. There, they may enter sensitive information, which will be stolen immediately.
Malware Distribution An attacker can tamper with a file or link that has been sent, injecting a virus, Trojan, or ransomware into the victim’s device.

The defining feature of MITM attacks is precisely their invisibility: everything appears to be functioning normally, making it difficult to detect them in time.

Digital security is not a luxury, but a necessity.

Man-in-the-middle attacks are insidious, but they can be recognized and prevented. It doesn’t take much to make the difference between a secure system and a vulnerable one.

Do you have questions about an invoice you received, or do you want to improve the security of your company’s communications? Contact us: our firm can help you protect your data, reputation, and peace of mind.

Types of Man-in-the-Middle Attacks

MITM attacks can take various forms, depending on the communication channel targeted, the context (public or corporate), and the attacker’s objectives. Understanding the main types helps identify them early on and defend against them effectively.

Wi-Fi MITM – Attack via an unsecured public network

This is one of the most common methods used in public places (cafés, hotels, airports, coworking spaces). The attacker sets up a fake Wi-Fi hotspot and gives it a name that is similar to or identical to that of a real network (e.g., “Free_Café_WiFi” instead of “Café_WiFi”).

When a user connects, Internet traffic passes through the attacker’s device, which can:

Monitor all browsing activity
Intercepting credentials and bank information
Redirect to fake websites

Avoid entering sensitive information on unsecured public networks. Use a VPN to encrypt your traffic, even in environments that appear to be secure.

Network spoofing – ARP and DNS spoofing

These are advanced techniques used to redirect internal network traffic, typically within a corporate or home network.

ARP Spoofing (Address Resolution Protocol): The attacker sends fake packets to the network, impersonating another device (e.g., the gateway). As a result, traffic between devices and the router is redirected to the attacker’s computer.
DNS Spoofing (Domain Name System): manipulates the mapping between a domain name and its IP address, redirecting the user to a website that looks identical to the original but is controlled by the scammer.

Common examples of network spoofing include accessing a banking or business portal that appears to be legitimate but is actually a malicious copy designed to steal credentials and sensitive data.

3. MITM in email – The so-called “Man in the Mail”

In this scenario, the attacker manages to intercept the email correspondence between two parties, usually by:

Interception of unencrypted SMTP traffic
DNS spoofing of the mail server
Compromise of one of the email accounts (actually a BEC attack, but with similar effects)

The main goal is to tamper with the content of communications: for example, by replacing the IBAN on an invoice or inserting malicious attachments.

MITM or BEC? Be aware of the difference

When discussing email scams—such as altered invoices or replaced IBANs—it is essential to distinguish between two scenarios that are often confused but technically different:

Business Email Compromise (BEC): The attacker gains direct access to a company’s or an employee’s email account (through phishing, malware, or stolen credentials). Once inside, they can read, send, or manipulate messages as if they were the legitimate user.
Man-in-the-Middle (MITM): The attacker does not have access to the accounts, but inserts themselves into the communication flow between the sender and the recipient, altering the messages in transit. The user is unaware that the content has been intercepted and modified before delivery.

Understanding this distinction is essential for implementing targeted security measures: protecting digital identities and access in the case of BEC; protecting network traffic and encrypting communication channels in the case of MITM.

Connection type	Technical Description	How it works	A typical scene
MITM (Man-in-the-Middle)	The attacker inserts themselves between the sender and the recipient without compromising them	Wi-Fi interception, protocol manipulation	The email is altered while in transit
BEC (Business Email Compromise)	The attacker directly targets the email inbox using phishing or malware	Direct access, reading, and sending from a legitimate account	The attacker modifies the invoice from within

4. HTTPS Stripping – Removal of Encryption

In this attack, the attacker forces the user’s browser to establish an unencrypted HTTP connection instead of the HTTPS version. This is possible on websites that do not enforce encryption (i.e., do not use the HSTS protocol—HTTP Strict Transport Security).

Once an unsecured connection is established, all data sent by the user (forms, credentials, messages) can be read in plain text by the attacker.

How can you protect yourself?
Browse only HTTPS sites: always check for the padlock icon in the address bar.
Avoid using public networks for sensitive transactions, especially without a VPN.
Install extensions such as HTTPS Everywhere (to force the use of encrypted connections whenever possible).
If you run a website, implement HSTS: it’s a technical measure that forces the browser to always connect via HTTPS.
Even a seemingly trustworthy website can become vulnerable if it is misconfigured. HTTPS only provides protection if it is actively enforced and properly implemented.

Do you want to protect your business from MITM attacks?

Request a cybersecurity assessment and find out if your communications are truly secure. Prevention is better than cure.

The Real Risks: What Can Happen in the Event of a Man-in-the-Middle Attack?

A man-in-the-middle (MITM) attack is not an abstract concept or something limited to high-tech environments: it can affect any individual, professional, or business that exchanges data online. The damage does not end at the moment of the attack, but can continue over time, resulting in financial losses, reputational damage, and serious legal consequences.

Theft of funds and fraudulent transactions

One of the most immediate risks is the direct theft of money, often by altering the bank account details on an invoice. The victim makes the payment, believing the account information to be correct, but the funds end up in the scammer’s hands.

Common examples:

Bank transfers to fake IBANs
Urgent requests regarding duplicate payments
Tampered invoices sent from compromised email accounts

In many cases, these funds are immediately transferred to foreign accounts or converted into cryptocurrency, making recovery difficult—if not impossible.

Breach of sensitive data

When an attacker manages to intercept or manipulate digital communications between two parties, they often gain access to a significant amount of confidential information. This isn’t just about isolated emails: we’re talking about conversation histories, company documents, contracts, strategic reports, and even sensitive data belonging to customers or employees—including personal, financial, or even health-related information.

Once stolen, this information never remains “static.” It can be used to orchestrate further scams, such as identity theft or social engineering attempts; sold on the dark web to criminal organizations; or publicly disclosed with the intent to damage the company’s reputation or blackmail those involved.

The biggest problem is that the damage isn’t limited to the moment of the attack: the consequences can linger over time, triggering a chain of new breaches, threats, and liabilities that are difficult to contain.

Unauthorized access to company systems

Once the attacker has obtained the login credentials, they gain access to a large amount of confidential data. This isn’t limited to individual emails; it often includes entire conversations, internal documents, contracts, and strategic analyses, as well as personal, financial, or health-related data pertaining to customers, employees, or partners.

Once obtained, this information does not remain dormant. It can be:

used for subsequent scams, such as identity theft or gaining access to new corporate systems,
resold on the dark web to international criminal groups,
or publicly disclosed to damage the company’s reputation or blackmail the victims.

The real danger is that the damage may not end with the initial attack. The consequences can snowball over time, triggering a chain of breaches, threats, and legal obligations that could seriously jeopardize the entire organization.

Reputational damage

Trust is at the heart of every professional relationship. A cyberattack often irreparably undermines this trust:

Customers are beginning to doubt the brand's reliability
Suppliers are demanding more guarantees
Stakeholders and investors may withdraw or renegotiate the terms

Rebuilding a reputation takes time, resources, transparency, and—in many cases—a costly crisis communication strategy.

Legal Liability and Penalties

When a man-in-the-middle attack results in a breach of personal data, a series of obligations under the General Data Protection Regulation (GDPR), which applies throughout the European Union, are immediately triggered.

Specifically, the affected organization is required to:

Report the incident to the data protection authority within 72 hours of discovery
Notify all individuals affected by the breach in a clear and timely manner
Demonstrate that you have implemented appropriate technical and organizational measures to prevent and mitigate damage

Otherwise, the company risks fines of up to €20 million or 4% of its global annual revenue —whichever is greater.

In addition to administrative penalties, civil and criminal liability may also apply, especially if negligence in security management is proven (e.g., outdated software, lack of encryption, absence of incident response plans).

How to Protect Yourself from a Man-in-the-Middle Attack
To protect yourself from a MITM attack, it is essential to adopt good digital habits and ensure that communications are always secure.
Start by checking that the websites you visit use HTTPS connections: the padlock next to the URL is a good first indicator of security. If possible, avoid public Wi-Fi networks or use a VPN, especially when accessing online banking, email, or sensitive data.
Keep your operating systems, antivirus software, and other software up to date, and enabletwo-factor authentication to add an extra layer of security to your most important accounts.
In your daily work, share sensitive information—such as bank details— only through secure, verified channels. If you receive a request to change your IBAN or an unusual message, contact the sender directly for confirmation using a phone number you already know.
Finally, to ensure the integrity and authenticity of communications, it is advisable to use digital signatures and encryption systems in business emails.

Man-in-the-Middle Attacks: Answers to Frequently Asked Questions.

What is a man-in-the-middle attack?

This is a cyberattack in which a malicious actor secretly intercepts communication between two parties —such as a customer and a supplier—to read, modify, or redirect the information being transmitted. The goal is to gain access to sensitive data, tamper with transactions, or compromise computer systems.

Are man-in-the-middle attacks common?

Yes, MITM attacks are more common than you might think, especially in situations where communications are not protected by end-to-end encryption. They are common on public Wi-Fi networks, in poorly secured corporate environments, and in combination with other techniques such as phishing or spoofing. They are used by both common cybercriminals and in digital espionage operations.

Is it possible to detect a man-in-the-middle attack?

In many cases, no—at least not right away. MITM attacks are designed to be invisible and silent. However, certain signs may raise red flags, such as:
– Invalid security certificates
– Insecure connections (lack of HTTPS)
– Anomalies in received messages (e.g., unusual language, changed IBAN)
– Emails that appear to have been read or deleted for no reason
Advanced enterprise security tools (such as intelligent firewalls and intrusion detection systems) can help detect suspicious behavior.

How are MITM attacks used in phishing campaigns?

A MITM attack can enhance phishing in two ways:
1. By intercepting traffic between the user and a fake website, thereby stealing credentials in real time.
2. By altering the content of legitimate emails, such as invoices or communications from suppliers, to insert fraudulent links or modified IBANs.
This makes phishing even harder to spot, because the attack exploits real conversations that are already taking place.

What is a man-in-the-middle attack?

“Man-in-the-middle” is a general term used to describe an attack in which an attacker interposes themselves between two parties who believe they are communicating directly with each other. It is an active interception technique that compromises the confidentiality and integrity of the communication.

How do MITM attacks work?

They work in two stages:
1. Interception: The attacker positions themselves between two parties (e.g., via a fake Wi-Fi network, ARP/DNS spoofing, or access to an email server).
2. Manipulation or monitoring: Once in the middle, they can read the transmitted data, modify it, or redirect it.
All of this happens without the sender or recipient noticing.

How does the TLS protocol prevent a man-in-the-middle attack?

TLS (Transport Layer Security) protects communications by encrypting them end-to-end. When enabled, it prevents an attacker from reading or altering data in transit, even if they manage to intercept it. In addition, TLS verifies the server’s authenticity using digital certificates, making it more difficult to use fake or compromised websites.

What is the most common type of man-in-the-middle attack?

The two most common forms are:
– Attacks on unsecured public Wi-Fi networks, where the attacker sets up fake hotspots to intercept traffic.
– Man-in-the-middle (MITM) attacks via email, often linked to corporate invoice fraud, in which the attacker alters payment details or sends forged communications.

What are the symptoms of an ongoing MITM attack?

Although often invisible, there are signs that should not be overlooked:
– Connections that seem slower or more unstable than usual
– Browser warnings about untrusted SSL certificates
– Emails with altered content or sent out of context
– Unusual behavior in email history
– Frequent errors when attempting to log in to secure portals

What is the main defense against a man-in-the-middle attack?

Strong encryption of network traffic, combined with valid digital certificates, serves as the first technical barrier. In practice, the combination of TLS, VPN, strong authentication, and staff training is the most effective way to reduce the risk of MITM attacks.