What’s the difference between credential theft and session hijacking?

Credential theft and session hijacking both let attackers impersonate users, but they exploit different weaknesses in the login process.

Key takeaways:

• Credential theft targets login details: Attackers steal usernames and passwords to access accounts, often through phishing or social engineering.
• Session hijacking targets active access: Attackers steal or manipulate session tokens to impersonate users who have already logged in.
• Multifactor authentication (MFA) helps, but it isn’t foolproof: Session hijacking can bypass MFA because the attacker is exploiting an already-authenticated session.
• Stopping these attacks requires layered defenses: Strong authentication, encryption, session monitoring, device checks, and user training all play a role.
• Zero trust reduces risk: Conditional, contextual access helps limit the damage if credentials or sessions are compromised.

Credential theft is one of the most common forms of cybercrime. Appearing in over 25% of data breaches, credential theft is also as simple as it gets:

1. Steal a username and password
2. Use it to log in somewhere you’re not supposed to
3. That’s it

Because credential theft is so common and usually the first thing most attackers will try, much of the fundamental cybersecurity toolkit consists of defenses against credential theft.

Session hijacking is different from credential theft. Although both session hijacking and credential theft allow an attacker to impersonate a user that’s logging in, session hijacking lets the attacker impersonate a user that has already logged in. This allows the attacker to circumvent many of the traditional controls against credential theft — and that’s why it’s important to tell these attacks apart.

Credential theft vs. session hijacking: Key differences

What is credential theft and how does it work?

Simply put, credential theft is when an attacker steals a user’s username and password and logs into a service to impersonate them. It’s one of the most common forms of cyberattack because credentials, unfortunately, are very easy to steal.

Phishing attacks are one of the most common mechanisms for credential theft. For example, a phishing victim may receive an email that appears to contain an important message from their bank. The victim clicks the link in the email and is redirected to a website that looks identical to their primary banking website. When they try to log in, the username and password fields harvest their information.

But credential theft is sometimes even easier. In several studies, users have been willing to trade their login credentials for money, for candy or just because they were asked.

How can organizations prevent credential theft?

Many defense techniques around credential theft are designed more closely around preventing its consequences. In other words, a technique like multifactor authentication (MFA) doesn’t prevent anyone from stealing credentials. Instead, it makes this attack vector useless to the attacker by introducing a new set of credentials that an attacker can’t easily steal.

For example, a technique like device fingerprinting collects the unique signature of a user’s phone, laptop or desktop based on its OS version, installed browser, physical location, and other factors. An attacker can steal a user’s credentials, but if they can’t replicate the device’s fingerprint, they’ll be forced to authenticate using a different factor such as biometrics or a one-time password. These factors aren’t impossible to steal (SMS-based verification is extremely vulnerable), but they’re more difficult than credential theft by itself.

Lastly, as far as preventing credential theft is concerned, security awareness training is one of the only effective methods of defense. If employees can recognize and flag phishing emails, their credentials will be exponentially harder to steal.

What is session hijacking and how does it work?

Session hijacking is a form of account impersonation that doesn’t (or doesn’t exclusively) rely on credential theft. Instead of impersonating a user at the credential level by inputting a stolen username and password, the attacker impersonates a user that is already logged in to an application or website. Here, the vulnerable credential is what’s known as a session token.

A session token effectively functions as a passport. It takes the form of a short code issued by a service that says “this user has valid credentials, has passed MFA and displays no unusual behaviors.” If your organization uses single sign-on (SSO), a session token is what lets you access a single service by only logging in once. Instead of asking you for a username and password, the connected services check for the presence of a valid session token and then log you in automatically.

If an attacker is able to intercept the session token, guess it by brute force or generate a valid token using specialized tools, then it can fool the system into thinking that they’re a valid user. Importantly, this method will not trigger MFA because the token contains information confirming that these factors have already been assessed.

How do attackers steal or abuse session tokens?

Attackers often use what’s known as a man-in-the-middle (MITM) attack to steal session tokens. For example, let’s say that a user is working from a coffee shop. The coffee shop Wi-Fi has been compromised, allowing an attacker to snoop on web traffic. As the user authenticates with a service, the attacker can intercept their session token and use it to perform a session hijacking attack.

Malware can also be used to carry out session hijacking attacks. If an attacker can inject malware into a user’s browser, they can intercept all web traffic, including session tokens. Alternatively, attackers may try to take advantage of website vulnerabilities with methods such as cross-site scripting. This forces a trusted website to deliver a hostile script to a logged-in user, which then scrapes the session token and returns it to the attacker.

Lastly, attackers may have the potential to generate their own valid session tokens. If an organization uses an insecure method to generate tokens, it can be possible for an attacker to predict what a valid token will look like. This will let them hijack a session without deploying any malware or exploiting any vulnerabilities.

How can organizations prevent and detect session hijacking?

There are two main avenues to mitigate session hijacking attacks: prevention and detection. Preventing session hijacking attacks means hardening connection and session infrastructure. Detecting session hijacking means flagging the suspicious behavior that surrounds a hijacked session.

Preventing session hijacking
A few relatively simple steps can dramatically increase the difficulty of session hijacking attacks, causing attackers to seek easier targets.

• Encryption enforcement: Encrypting traffic — including session cookies — with protocols such as TLS/SSL will ensure that intercepted tokens become useless to attackers.
• Session management: If a token expires after 15 minutes of inactivity, an attacker will have a much shorter window to exploit a captured credential.
• Awareness training: Working from a coffee shop is an attractive idea, but public Wi-Fi is never secure. Train users to always use a VPN.
• Detecting session hijacking
  Hijacked sessions don’t behave like normal users. By adding a set of rules to your SIEM tool, you can flag session hijacking attacks before attackers can damage your files or steal proprietary information.
• Behavior monitoring: Hijacked sessions behave in unusual ways. They’ll attempt to encrypt, delete, move, or exfiltrate files. They may try to access applications they don’t have access to or escalate their privileges. Learn to alert on these signals.
• Device monitoring: Hijacked devices will also display unusual behaviors. Look for users suddenly switching locations or devices in ways that are impossible (e.g. instantaneous travel from NYC to London).
• Session monitoring: Lastly, hijacked sessions will look very strange under scrutiny. A textbook example is the same user opening two different sessions from two different systems.

How zero trust access helps reduce session hijacking risk

Unfortunately, the prevalence of session hijacking and credential theft means that no user, no matter how thoroughly authenticated, should ever be fully trusted. With that in mind, Barracuda offers SecureEdge Access, a powerful zero trust network access (ZTNA) solution that delivers high speeds and powerful end-to-end encryption. Designed to replace the pitfalls of a traditional VPN, SecureEdge Private Access provides remote, conditional and contextual access to resources, minimizing the risk of session hijacking.

There are many ways to prevent session hijacking, and many ways to detect it after the fact. SecureEdge Access combines these methods into a single tool designed to prevent attackers from circumventing MFA and impersonating trusted users. Sign up for a free trial and learn how easy it is to safeguard your sessions.

Credential theft and session hijacking FAQ

Is session hijacking the same as credential theft?

No. Credential theft happens when an attacker steals login details such as a username and password. Session hijacking happens when an attacker steals or manipulates a valid session token after the user has already logged in.

Can session hijacking bypass MFA?

Yes, session hijacking can bypass MFA in some cases because the attacker is abusing an already-authenticated session. If the session token shows that MFA has already been completed, the application may not prompt for MFA again.

What is a session token?

A session token is a temporary digital identifier that tells an application a user has already logged in successfully. It allows the user to stay authenticated without re-entering their credentials for every action or connected service.

How can businesses detect session hijacking?

Businesses can detect session hijacking by monitoring for unusual session behavior, such as impossible travel, simultaneous sessions from different devices, unexpected privilege escalation, abnormal file activity, or access attempts from unfamiliar locations.

What is the best defense against credential theft and session hijacking?

The best defense is a layered security strategy. MFA, password hygiene, user training, and conditional access help reduce credential theft, while encryption, secure session management, session monitoring, device monitoring, and zero trust access help reduce session hijacking risk.