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You have a strong password. You use multi-factor authentication (MFA). So, if a hacker doesn’t have your password or access to your MFA code, they can’t get into your account, right? Unfortunately, session hijacking can change that equation.

An attacker can take over an already authenticated session. In some cases, that means the hacker doesn’t need your password. They don’t need your MFA code, either. You already did the work of proving your identity for them.

Think about getting a wristband at an event. You show your ticket at the entrance, prove you belong there, and receive a wristband. For the rest of the event, that wristband tells security you’ve already been checked.

Your browser does something similar after you log in to an online account. It receives a session token—often stored in a cookie—that tells the website you have already authenticated. If an attacker steals that digital “wristband,” the system may treat them as though they already passed the same security checks you did.

That doesn’t mean MFA doesn’t work. MFA remains one of the most important protections a business can use. But session hijacking demonstrates why no single cybersecurity measure should stand alone.

Let’s look at how session hijacking works, how attackers steal authenticated sessions, and what businesses can do to make those attacks much harder to pull off.

What Is Session Hijacking?

Every time you log in to an online account, the website needs a way to remember that you already proved who you are. Otherwise, you would have to enter your password and complete MFA again every time you opened an email, viewed a file, or clicked another page.

That’s where your session comes in.

After you successfully log in, the service gives your browser a session token. Think back to that event wristband. The token tells the service, “This person already passed the security check. They can come in.”

Normally, that makes using online accounts faster and easier. The problem begins when someone else gets that token.

With session hijacking, an attacker steals or intercepts a valid session token and attempts to reuse it. Because the token belongs to an already authenticated session, the service may recognize the attacker as the legitimate user instead of asking for a password or another MFA approval.

Microsoft explains that stolen authentication tokens can allow an attacker to impersonate a user, potentially giving them unauthorized access to the user’s data and resources.

And that is an important distinction: the attacker hasn’t necessarily defeated MFA.

MFA may have worked exactly as intended when you signed in. Instead of breaking through that security check, the attacker stole the digital proof that says you already passed it.

That’s what makes session hijacking both effective and easy to misunderstand.

How Does Session Hijacking Happen?

Knowing that a session token can act like a digital wristband raises an obvious question: How does a hacker get it in the first place?

There isn’t just one method. Attackers can use phishing, compromised devices, malicious software, and other techniques to steal session information. Here are a few ways it can happen.

1. A Convincing Phishing Attack

Some modern phishing attacks do much more than collect usernames and passwords.

In an adversary-in-the-middle (AiTM) attack, a hacker places a malicious site between you and the legitimate service you are trying to access. The fake login experience may look and behave like the real one because information is being passed between you and the legitimate website in real time.

You enter your username and password. You complete the MFA request. You may even successfully reach the account you intended to visit.

Meanwhile, the attacker captures the authentication token created during that successful sign-in.

Microsoft documented a 2026 phishing campaign that used this technique to capture authentication tokens and compromise accounts.

That’s part of what makes these attacks so dangerous. From the employee’s perspective, MFA worked. They completed the security step exactly as expected. The attacker simply positioned themselves where they could steal what came next.

2. Malware on a Computer

Attackers can also steal session information directly from a compromised device.

Malware designed to steal information may be able to access authentication tokens, browser cookies, saved credentials, and other valuable data. That means an attacker doesn’t necessarily have to trick you into entering your information on a fake login page. If malicious software is already running on the computer, it may be able to steal an active session from there.

This is one reason protecting the device itself matters just as much as protecting the password used on it.

3. Risky Browser Extensions and Other Software

Browser extensions can be incredibly useful, but they also operate inside the same browser you use to access email, cloud applications, financial information, and other business systems.

An extension that is malicious, compromised, or given more access than it needs can create another opportunity for sensitive browser data to be exposed. That doesn’t make every browser extension dangerous. It does mean businesses should know which extensions employees are installing and what permissions those extensions receive. The same concern applies when employees install unapproved software or tools without considering what information those applications can access.

The common thread is simple: attackers don’t always need to break down the front door. Sometimes they look for a way to steal the proof that someone else already unlocked it.

What Can a Hacker Do After Session Hijacking?

Stealing a session token is only the beginning. The real danger comes from what the attacker may be able to access once the system recognizes them as the legitimate user.

Exactly what they can do depends on the account and the permissions that user has. But if the stolen session provides access to business email, cloud storage, or other company systems, the consequences can spread quickly.

An attacker may be able to:

• Read business email. That can expose private conversations, customer information, invoices, contracts, and other sensitive data.
• Send messages as the employee. A message coming from a legitimate company account can be far more convincing than one coming from an unfamiliar address.
• Access files and cloud applications. If the employee’s authenticated session includes access to company data, the attacker may inherit some of that access.
• Look for financial opportunities. Email conversations involving invoices, payments, vendors, payroll, or wire transfers can give an attacker the information needed to attempt fraud.
• Use one compromised account to target others. Access to a trusted employee’s account can help an attacker create convincing messages aimed at coworkers, customers, or vendors.

This is where session hijacking can turn into something much larger than one compromised login. An attacker who gains access to a legitimate account can observe how your business communicates, learn who handles money or sensitive information, and use that knowledge to make the next attack much more convincing.

That can also lead to business email compromise (BEC), where criminals use trusted business accounts or identities to manipulate employees, customers, or vendors into sending money or sensitive information.

The attacker didn’t necessarily crack a password. They didn’t necessarily defeat MFA.

They stole the wristband—and then started walking through every door it opened.

Why MFA Still Matters

After learning that session hijacking can sometimes bypass the normal login process, it would be easy to wonder whether MFA is still worth using.

Absolutely.

Multi-factor authentication remains one of the most effective ways to protect accounts from stolen or compromised passwords. If an attacker gets your password but cannot complete the additional authentication step, MFA can stop that stolen password from becoming a stolen account.

Session hijacking doesn’t make MFA ineffective. It targets a different part of the process.

Remember our event analogy: MFA helps make sure the right person receives the wristband at the entrance. Session hijacking happens when an attacker finds a way to steal that wristband after it has already been issued.

That distinction matters because cybersecurity works best in layers. Strong passwords and MFA protect the login process. Device security, phishing protection, access controls, session management, and ongoing monitoring help protect what happens before, during, and after that login.

The goal isn’t to replace MFA. It’s to make sure MFA isn’t standing guard all by itself.

How Businesses Can Reduce the Risk of Session Hijacking

There is no single setting that eliminates the risk of session hijacking. Instead, businesses can make these attacks much harder by protecting the different places an attacker might use to gain access.

Protect the Devices Employees Use

A secure login can only do so much if the computer itself is compromised.

Keep operating systems, browsers, and business applications updated. Use endpoint protection that can detect malicious activity, and make sure employees aren’t working from unmanaged or poorly protected devices.

This becomes even more important when employees work from home, travel, or access company systems outside the office. Securing company laptops for remote employees can help reduce the opportunities attackers have to compromise the device in the first place.

Make Phishing Harder to Pull Off

Traditional MFA still provides important protection, but businesses can strengthen authentication further with phishing-resistant options.

Passkeys and hardware security keys, for example, can provide stronger protection against phishing attacks because authentication is tied to the legitimate website rather than relying on a code an employee can unknowingly provide through a fake login page.

Technology isn’t the only piece. Employees should also know that a login page can look completely legitimate and still be part of an attack. Unexpected login prompts, unfamiliar links, and unusual requests to sign in deserve a closer look.

Know What Is Running in the Browser

Browsers have become a gateway to email, cloud storage, accounting platforms, customer data, and countless other business systems.

Businesses should know which browser extensions and applications employees are using, particularly when those tools request access to website data. Limit unnecessary extensions and software, and periodically review what has been installed.

Use Access and Session Controls

Businesses using platforms such as Microsoft 365 can apply policies that consider more than whether someone entered the correct password.

Depending on the environment, organizations may be able to restrict access based on factors such as the device being used, the user’s location, sign-in risk, or other unusual activity. Session controls can also limit how long access remains valid or require users to authenticate again under certain circumstances.

These controls help reduce how much an attacker can accomplish with a stolen session.

Watch for Signs of Suspicious Access

Prevention matters, but so does noticing quickly when something gets through.

Unusual sign-in locations, unfamiliar devices, unexpected changes to an account, suspicious email activity, or access patterns that don’t fit an employee’s normal behavior can all warrant investigation.

The sooner suspicious activity is identified, the sooner your IT team can contain it and determine what happened.