How Attackers Mimic Legitimate Users After Account Takeovers

Summary: Attackers use sophisticated methods to mimic legitimate users after an account takeover, making detection difficult, but AI-driven behavioral analysis offers a solution by establishing user baselines and identifying subtle anomalies.

An account takeover (ATO) is more than just a security breach; it's the start of a covert operation. Once an attacker gains unauthorized access to a user's account, their primary goal is to remain undetected for as long as possible. To do this, they've become masters of disguise, carefully mimicking the behavior of the legitimate user to blend in with normal activity. This makes detecting their presence incredibly difficult for security teams relying on traditional tools, which often focus only on the initial point of entry. Understanding how attackers "live off the land" inside your cloud environment is the first step to effectively detecting and stopping them.

The Initial Breach: A Foot in the Door

Before an attacker can mimic a user, they first need to steal their keys. Corporate Account Takeover (CATO) attacks typically begin by exploiting the weakest link: human behavior or credential hygiene. Attackers have a well-established playbook for gaining that initial foothold.

Common entry vectors include:

• Phishing: Crafting convincing emails that trick users into revealing their credentials on a fake login page.
• Password Reuse: Exploiting credentials leaked from a breach on another, less secure website that the user also used for their corporate account.
• Brute-Force Attacks: Systematically trying different password combinations until they find the right one, often targeting accounts with weak passwords.‍
• Social Engineering: Manipulating users to bypass security controls, including tricking them into approving a multi-factor authentication (MFA) push notification.
  

Once they're past the front door, the real infiltration begins.

The Art of Invisibility: Attacker Tactics Post-Compromise

An attacker's post-compromise strategy is all about stealth. They know that loud, aggressive actions will trip alarms. Instead, they adopt a "low and slow" approach, using the compromised account's existing access and tools to carry out their objectives without raising suspicion.

Living Off the Land

This technique involves using an organization's own systems and tools against itself. From a security monitoring perspective, the attacker's actions look almost identical to the legitimate user's.

• Searching for Treasure: One of the first things an attacker does is search the user's email and files for sensitive information. They'll look for documents containing passwords, financial data, intellectual property, or customer lists. This search activity can easily be mistaken for an employee looking for a file they need for their job.
• Manipulating Email Rules: A classic and highly effective tactic is to create new email rules. An attacker might set up a rule to auto-forward copies of all incoming messages to an external account. They might also create a rule to immediately delete any emails from the IT or security team that mention password resets or suspicious activity, effectively hiding their tracks from the real user.
• Pivoting to Other Apps: A compromised email account is often the key to a much larger kingdom. Attackers will use the "Forgot Password" feature on connected applications, intercepting the reset link sent to the compromised inbox. This allows them to pivot and gain access to other sensitive corporate systems, from HR platforms to financial software.
  

Exploiting Shadow IT

The rise of unsanctioned cloud applications, or "Shadow IT," adds another layer of complexity. When employees connect third-party apps to their corporate accounts, they create new, often unmonitored, pathways for data access. Attackers can exploit these existing connections to exfiltrate data or move laterally in a way that blends in with normal, albeit unsanctioned, user activity.

The Challenge with Traditional Security: Legacy security tools are often blind to this subtle, post-login activity. They might successfully flag a suspicious login from a new country, but they typically lack the context to understand if a user suddenly creating a new email forwarding rule is a sign of compromise or a legitimate productivity hack.

A Modern Approach: Detecting the Undetectable with Behavioral Analysis

Because attackers are so adept at mimicking users, you can no longer rely solely on preventative controls like MFA and strong passwords. While essential, they are not foolproof. The key to catching a disguised attacker is to move beyond static rules and embrace a dynamic, behavioral approach to security.

Establishing a Behavioral Baseline

Modern security platforms use AI and machine learning to build a unique behavioral profile for every user in your organization. Think of it as learning each employee's digital rhythm. This baseline includes dozens of signals, such as:

• Typical login times and locations
• Commonly used devices
• Normal email sending and reading patterns
• Frequently accessed applications and files
  

This rich, contextual baseline is the foundation for spotting what’s out of place.

Identifying Subtle Anomalies

With a baseline of normal behavior established, a platform can instantly flag subtle deviations that, on their own, might seem harmless but are highly indicative of an ATO when correlated.

Key indicators of compromise include:

• Suspicious Logins: A login from a new, high-risk location or at an unusual time of day.
• Anomalous Message Retrieval: An unusual spike in the number of emails being read or downloaded, which could signal an attacker searching the mailbox.
• Suspicious Rule Creation: The sudden appearance of an email rule that forwards or deletes messages.
• Failed Data Access: An attempt to access a sensitive file that the user has never touched before.
  

By combining evidence—for example, a suspicious login followed by the creation of a forwarding rule—the system can raise a high-fidelity alert that an incident response team can act on immediately.

Containing the Blast Radius Before It's Too Late

Detection is critical, but it's only half the battle. The ultimate goal is to contain the threat and minimize the damage. This is where a unified platform that combines detection with automated response becomes invaluable.

Even if an attacker successfully compromises an account, advanced security platforms can severely limit what they can do next. For example, some solutions can automatically challenge attempts to access sensitive historical data within a mailbox, requiring step-up authentication even if the attacker has the user's password. Furthermore, they can prevent attackers from using the compromised inbox to receive password reset links for other applications, effectively shutting down their ability to move laterally and expand their breach. This automated containment gives security teams the breathing room they need to investigate and remediate the incident without the attacker causing further harm.

Take Control of Your Cloud Workspace Security

Attackers will continue to evolve their tactics, becoming ever more skilled at blending into your environment. To stay ahead, you need a security solution that can see beyond the perimeter and understand the nuances of user behavior. By leveraging AI-driven behavioral analysis, you can unmask attackers who are trying to hide in plain sight.

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