Beyond MITM: The Rising Danger of Adversary-in-the-Middle Attacks

You’ve almost certainly heard of man-in-the-middle (MITM) attacks. But recently a new, similar but more advanced and dangerous attack type has emerged: adversary-in-the-middle (AITM).

The two attack types are structurally similar. But their mechanics, sophistication and capabilities are decidedly different. For IT admins, understanding this distinction, and how each type of attack operates, is critical to keeping your systems and data secure.

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

MITM attacks are a longstanding technique for intercepting valuable information in transit. In this scenario, a malicious actor secretly relays and possibly alters the communication between two parties who believe they are directly communicating with each other. Think of it as someone eavesdropping on a private conversation and occasionally chiming in with misleading information.

MITM attacks typically exploit unsecured or poorly secured networks, such as public Wi-Fi. They may also rely on DNS spoofing, ARP poisoning, or SSL stripping to intercept traffic. The attacker might capture login credentials, session cookies or sensitive data in transit. However, most modern web services use HTTPS and other encryption protocols that make traditional MITM attacks increasingly difficult to execute successfully.

What is an adversary-in-the-middle attack?

AITM attacks are the next evolution of MITM tactics: more sophisticated, more targeted and more dangerous. In an AITM attack, the adversary doesn’t just passively intercept traffic. Instead, they actively manipulate the authentication process, which makes them capable of bypassing multifactor authentication (MFA) schemes.

AITM attacks typically involve phishing campaigns that direct users to a proxy server controlled by the attacker. This proxy sits between the user and the legitimate service (e.g., Microsoft 365 or Google Workspace), capturing credentials and session tokens in real time. Because the attacker is relaying the session live, they can bypass MFA by capturing the token after the user completes the second authentication step.

Key differences between MITM and AITM

Why AITM is more dangerous

AITM attacks are particularly dangerous because they exploit trust at the application layer. Even if your organization enforces MFA, AITM can render it ineffective. Once an attacker has a valid session token, they can impersonate the user without needing to re-authenticate.

Moreover, AITM attacks are harder to detect. Since the attacker is relaying legitimate traffic, traditional network monitoring tools may not flag the activity as suspicious. The user sees a familiar login page, completes MFA and continues on, unaware that their session has been hijacked.

Real-world examples

AITM attacks aren’t theoretical — they’re happening right now.

• In 2024, Microsoft 365 was targeted by attackers using a phishing-as-a-service (PhaaS) toolkit called Rockstar 2FA. A Microsoft employee was tricked into authenticating through a fake site, handing over their session token in the process.
• Storm-0485, a known threat actor, has used AITM techniques to harvest credentials at scale. Their campaigns often use fake LinkedIn verification emails and obfuscated URLs to lure users into giving up access.

The frequency of AITM attacks is rising rapidly due to their ability to bypass traditional access controls such as MFA and encryption protocols such as HTTPS.

How to defend against AITM

A modern, multilayered cybersecurity platform like BarracudaONE provides the best defense against AITM and other sophisticated attacks. Strong email protection such as Barracuda Email Protection lets you spot and block initial phishing attempts, while powerful network security like Barracuda Network Protection delivers advanced zero-trust network access controls that go beyond MFA to identify and block unauthorized access to resources, even when legitimate credentials are presented.