Between You and the Data: Defending Against Man-in-the-Middle Attacks

Despite the widespread adoption of encryption and authentication protocols, man-in-the-middle (MITM) attacks remain one of the most persistent and dangerous threats in cybersecurity. These attacks don’t rely on brute force. They exploit weak links in visibility, validation, and communication flow. Whether it’s an attacker silently eavesdropping on a conversation or actively modifying traffic between users and services, MITM attacks allow adversaries to intercept sensitive data, hijack sessions, or inject malicious payloads without ever being detected.

The opportunities for MITM attacks multiply as organizations become more connected via APIs, SaaS platforms, remote access, and cloud-native infrastructure. Trusting that encryption alone is doing its job is no longer enough. Modern defense requires context-aware monitoring, strong configuration hygiene, and early detection capabilities to uncover subtle signs of interception before they escalate into breaches.

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

A MITM attack happens when an attacker secretly intercepts communication between two parties, like a user and a website, without their knowledge. Sometimes, the attacker simply listens; other times, they alter the data being exchanged.

MITM attacks are especially dangerous because they exploit trust. Everything appears normal to the user, while sensitive data like credentials or financial information is silently captured or manipulated. In both consumer and enterprise environments, this can lead to stolen accounts, data breaches, or unauthorized access, often without immediate detection.

How does a MITM attack work?

At a high level, a MITM attack follows a deceptively simple process. First, the attacker positions themselves between two endpoints: a user, a website, a remote employee, and a corporate server. This can happen through ARP spoofing, DNS hijacking, or by setting up a rogue Wi-Fi access point.

Once in position, the attacker intercepts the communication by silently capturing or manipulating data. They may redirect traffic, inject malicious code, or tamper with real-time requests and responses.

The result? Data is harvested, altered, or exploited while users believe their connection is secure.

Passive vs. active MITM attacks

MITM attacks generally fall into two categories: passive and active, and understanding the difference is key to identifying their impact.

In a passive MITM attack, the attacker acts as a silent observer. They monitor traffic between two parties without altering the content. This type of eavesdropping is often used to harvest login credentials, session tokens, or personal information, all without alerting the victim.

On the other hand, an active MITM attack goes a step further. Instead of just watching, the attacker begins modifying or injecting data into the communication stream. This could mean redirecting a user to a fake login page, altering financial transactions, or inserting malicious payloads into a seemingly legitimate exchange.

What’s particularly dangerous is that many MITM attacks begin as passive reconnaissance. Once attackers gather enough insight, they often escalate to active manipulation, turning silent observation into direct exploitation.

Common MITM attack vectors and techniques

MITM attacks can take many forms, often depending on the attacker’s proximity to the target and the level of control they can gain over the network or endpoint. Here are some of the most common MITM attack vectors and techniques used in the wild:

• ARP spoofing: Attackers exploit the Address Resolution Protocol (ARP) by sending false ARP messages on a local network. This tricks devices into sending traffic to the attacker’s MAC address instead of the intended destination, allowing full visibility into network communication.

• DNS spoofing: In this technique, the attacker responds to a DNS request with a forged IP address, redirecting users to malicious or lookalike websites. It’s often used with phishing, credential harvesting, or SSL strip attacks that downgrade secure HTTPS connections to insecure HTTP.

• Wi-Fi-based attacks: Attackers set up rogue access points, often mimicking legitimate networks (so-called Evil Twin attacks). Unsuspecting users connect, unknowingly routing their data through the attacker’s system. Even well-meaning public Wi-Fi can be exploited if it lacks strong encryption.

• SSL/TLS attacks: These attacks compromise the trust model of HTTPS through SSL stripping, expired or forged certificates, or poor certificate validation on the client side. This lets attackers view or manipulate supposedly secure data in transit.

• Session hijacking: Here, attackers intercept or steal session cookies or tokens, granting them access to authenticated sessions without needing credentials. In session fixation, a victim is tricked into using a session ID that the attacker already controls.

• Man-in-the-browser attacks: Malware modifies web traffic from within the user’s browser, often in the form of malicious browser extensions or injected proxy scripts. This allows attackers to alter form data, manipulate transactions, or silently exfiltrate sensitive information as the user interacts with trusted applications.

Each technique can be devastating individually, but many attackers chain them together, moving from passive observation to active exploitation with alarming speed.

Real-world impact: MITM case studies

MITM attacks aren’t just theoretical. They’ve played a central role in recent years’ most costly and sophisticated breaches. Their quiet nature and adaptability make them effective across various targets, from individual users to entire enterprises.

Financial sector attacks

MITM techniques have been used to hijack active banking sessions, exploit insecure APIs, and inject malicious scripts on the client side. Attackers intercept transactions, manipulate data in real-time, and harvest session tokens, all while remaining undetected by users and institutions.

Cryptocurrency exchange vulnerabilities

With crypto, MITM attacks often involve DNS spoofing or wallet redirection, tricking users into sending funds to attacker-controlled addresses. Even personal wallets connected to insecure networks have been compromised without breaching the exchange.

Corporate espionage & IP theft

State-sponsored attackers have used MITM tactics to intercept proprietary data via compromised VPN tunnels or rogue Wi-Fi networks. These attacks target internal documents, trade secrets, and communications, often leaving no immediate trace.

Supply chain compromise

MITM positioning during software delivery or vendor API interactions allows attackers to alter packages in transit, inject malicious code, or steal credentials, impacting not just one company but its entire downstream ecosystem.

MITM tools and techniques

It is helpful to examine the tools that enable MITM attacks to understand how they happen. Initially designed for legitimate security testing and network diagnostics, many of these tools are repurposed by attackers in the wild.

Tools like Ettercap and Bettercap are widely used for ARP spoofing, DNS spoofing, and traffic manipulation on local networks. Wireshark, a powerful packet analyzer, can passively capture and inspect network traffic, often as the first step in identifying exploitable patterns. Dsniff and Cain & Abel offer credential sniffing and network-based password cracking features. At the same time, SSLSplit enables attackers to intercept and decrypt HTTPS traffic by acting as a rogue proxy between clients and servers.

While these tools are perfectly legal and valuable in penetration testing and red team exercises, they’re also readily available and well-documented, making them a double-edged sword in adversaries’ hands. Knowing how they work is crucial for defending against MITM attacks and detecting them before damage is done.

How to detect a man-in-the-middle attack

Detecting a Man-in-the-Middle (MITM) attack isn’t always straightforward, but several red flags can indicate something’s wrong:

• Certificate warnings or mismatched domains: Unexpected SSL/TLS certificate errors when visiting trusted sites may signal HTTPS interception.

• Unusual redirects or DNS changes: Landing on incorrect or suspicious websites could point to DNS spoofing or redirection through a rogue server.

• Duplicate IPs or strange ARP entries: Conflicting IP addresses or odd MAC address mappings often indicate ARP spoofing on local networks.

• SSL/TLS downgrade attempts: A forced switch from HTTPS to HTTP or from TLS 1.3 to older protocols can signal an SSL stripping attempt.

• Alerts from security tools: Endpoint detection systems, IDS solutions, or cloud monitors may flag anomalies like certificate mismatches, unauthorized proxy usage, or unexpected session behavior.

While none of these signs confirm a MITM attack on their own, spotting more than one in tandem should raise serious concerns.

Mitigation and prevention strategies

Preventing MITM attacks requires a mix of strong encryption, secure configurations, and continuous monitoring. Key strategies include:

• Use strong encryption protocols: Enforce TLS 1.3 or higher to protect data in transit and prevent downgrade attacks.

• Enforce certificate pinning and validate public keys: This helps ensure the authenticity of connections and blocks forged certificates.

• Use trusted VPNs: A verified, secure VPN can protect communications over untrusted networks only if configured and maintained properly.

• Implement multi-factor authentication (MFA): MFA adds a critical layer of protection, reducing the risk of session hijacking or credential theft.

• Monitor for DNS and ARP anomalies: Use network monitoring tools to detect spoofing attempts or unexpected routing behavior.

• Scan dependencies and third-party tools: MITM risks can be introduced through compromised libraries or tools, especially those handling network traffic or proxies.

Together, these controls reduce the likelihood and potential impact of MITM-based threats.

Key takeaways

• MITM attacks exploit insecure connections to intercept or manipulate user data.

• Techniques range from ARP spoofing to browser injection to DNS and SSL exploits.

• Detection requires both network-level monitoring and secure code practices.

• Snyk helps secure code, infrastructure, and third-party risk to reduce MITM exposure.

Mitigate and prevent MITM attacks with Snyk

Preventing MITM attacks starts with securing the code, infrastructure, and third-party components that make up your application, and Snyk helps teams do just that.

Snyk Code identifies risky patterns like weak cryptography, improper validation, and exposed secrets issues that attackers often exploit to enable MITM positioning.

Snyk IaC scans infrastructure code for misconfigurations, such as open ports, unencrypted traffic, and permissive network policy conditions that create ideal entry points for interception.

Snyk AppRisk adds visibility into app-level risk, flagging insecure dependencies and misused integrations that attackers can leverage during MITM attacks.

Snyk also tracks evolving threats, from AI-assisted attacks that generate realistic phishing flows to agent hijacking and LLMjacking, modern techniques that often rely on MITM-style interception.

By combining static analysis, infrastructure scanning, and deep application context, Snyk helps teams stay one step ahead, blocking MITM threats before they take hold.

Start building secure-by-default systems and keep attackers out of the middle with Snyk. Learn more about our appsec solutions today.