Session Hijacking

Session hijacking is a cyberattack in which bad actors gain unauthorized access to a user’s active website or application session. These attacks exploit vulnerabilities in web session management by enabling the cyberattacker to impersonate a legitimate user.

At its core, session hijacking involves intercepting or guessing the session identifier, a unique token assigned to a user upon login. Obtaining access to this identifier enables the attacker to assume the user’s identity within the system, potentially accessing sensitive information, making unauthorized transactions, or performing other malicious actions. 

Session hijacking attacks can have severe consequences, including data breaches, financial losses, and compromised user privacy. They pose a significant risk to organizations and individuals alike, particularly in scenarios involving sensitive data like online banking or confidential corporate files.

• Cyberattackers use session hijacking to gain unauthorized access to a user’s active website or application session. 
• Cybercriminals execute session hijacking by waiting for users to authenticate themselves on a website or app. They can then intervene in the users' normal activity and gain unauthorized access to sensitive information by impersonating them digitally. 
• Individuals and corporations should take session hijacking attacks seriously, as they can lead to expansive data breaches, financial loss, and reputational damage.

In IT, a session is defined as a temporary, interactive information exchange between a user’s browser and a web server. It begins when a user logs into a website or application and ends when they log out or their session times out automatically after a period of inactivity.

Sessions are crucial for maintaining state in the stateless HTTP protocol. They allow websites to remember user-specific information and preferences across multiple page requests. This accounts for custom user experiences, such as keeping items in a shopping cart or maintaining login status.

When a session starts, the server typically generates a unique session ID. This ID is often stored on the client side as a cookie or appended to URLs. The server uses this ID to associate the user with their specific server-side data.

Sessions enhance user experience and enable complex web application features, but it’s important to manage them securely to prevent various cyberattacks, including threat actors that may want to hijack a session.

As with many cyberthreats, the best time to stop session hijacking is before it starts. Doing so requires understanding how these attacks occur so we can spot their signals as early as possible. Typically, a session hijacking attack will follow these steps:

• Initial authentication: The legitimate user enters their credentials to log into a website or application. The server verifies these credentials and establishes a new session connection for the user.
• Session ID generation: Upon successful authentication, the server creates a unique session identifier. This ID is typically a long, random string intentionally designed to be challenging to guess. The server sends this ID to the user's browser, where it’s usually stored as a cookie.
• Normal user activity: The authenticated user interacts with the website or application. Each request they make to the server includes the session ID, allowing the server to assign that particular request to the user’s authenticated session and maintain their state.
• Attacker intervention: The attacker uses sophisticated techniques to predict or intercept the session ID. Some techniques they might use include exploiting network vulnerabilities, leveraging malware, or exploiting weaknesses in the website’s session management system.
• Session ID acquisition: The attacker successfully obtains a valid session ID through one or more attack vectors. They can accomplish this through real-time interception or by exploiting predictable session ID generation patterns.
• Impersonation: The attacker crafts requests to the server that include the stolen session ID. These requests appear to come from the legitimate user from the server’s perspective, as the session ID is valid.
• Unauthorized access: The server processes the attacker’s requests as if they were from a legitimate user. This grants the attacker the same access and privileges as the original user, potentially compromising sensitive data or functionality.
• Malicious activities: With full access to the user’s session, the attacker can perform various unauthorized actions. These may include viewing or modifying personal information, initiating financial transactions, or using the compromised account to launch further attacks.
• Session termination: The hijacked session ends either when the legitimate user logs out (potentially locking out the attacker), when the session naturally expires due to inactivity, or when the attacker ends their malicious activities to avoid detection.

Not all session hijacking attacks are the same. Cybercriminals have a tool belt of tactics to access user sessions depending on circumstances or their end goals. Here’s a more in-depth look at each of them.

Cross-site scripting (XSS)

Attackers exploit vulnerabilities in web applications to inject malicious scripts into pages viewed by users. They can use these scripts to steal session IDs directly from the user's browser. XSS attacks bypass the same-origin policy, allowing attackers to access sensitive data and hijack user sessions under the radar without directly compromising the server.

Session fixation

Attackers establish a valid session ID and trick users into authenticating with it. This is often done by sending a malicious link containing a predetermined session ID. Once the user logs in, the attacker gains access to the authenticated session, bypassing the need to steal credentials or guess session IDs.

Session sidejacking (session sniffing)

Cybercriminals can intercept network traffic to capture session cookies on unsecured Wi-Fi networks. They use packet sniffing tools to monitor data transmissions and extract session IDs from unencrypted traffic. This method is particularly effective when only the login page is encrypted. Any requests a user makes on subsequent pages are vulnerable.

Man-in-the-browser

This attack involves malware infecting the user’s browser. The malware intercepts and modifies web transactions in real time, allowing attackers to manipulate session data, alter transaction details, or create unauthorized transactions. Man-in-the-browser attacks can be challenging to detect, as requests originate from the victim’s computer and appear legitimate to web services.

Predictable session token IDs

This attack exploits weak algorithms used by web servers to generate session IDs. Attackers analyze patterns in existing IDs to predict future ones. They may leverage flaws like time stamps, sequential numbers, or weak random number generators. Once cybercriminals decipher the pattern, they can generate valid session IDs to hijack active user sessions without needing to intercept or steal tokens.

Session hijacking can have severe consequences for both individuals and organizations. Here are five significant impacts of successful session hijacking attacks:

• Data breach: Attackers can access sensitive personal or corporate information, potentially leading to identity theft, financial fraud, or corporate espionage.
• Financial loss: Hijackers may initiate unauthorized financial transactions, transfer funds, or make purchases using the victim’s account credentials.
• Reputational damage: Organizations that fall victim to session hijacking may significantly damage their reputation, leading to loss of customer trust and potential revenue.
• Unauthorized system access: In cases where single sign-on (SSO) is implemented, a hijacked session could grant attackers access to multiple systems, exponentially increasing the potential damage.
• Compliance violations: Depending on the industry and type of data compromised, session hijacking incidents may result in violations of data protection regulations, leading to legal consequences and significant fines or sanctions.

Now that you know what session hijacking attacks might look like “on paper,” let’s look at real-world examples. 

Zoom bombing

During the COVID-19 pandemic, video conferencing platforms like Zoom became targets for session hijackers. Attackers exploited vulnerabilities in meeting settings to gain unauthorized access to private video sessions. Some hijackers would disrupt meetings by shouting profanities, sharing offensive content, or displaying lude images.

This phenomenon, dubbed “Zoom bombing,” highlighted the importance of robust web application security measures in virtual communication tools. In response, Zoom implemented enhanced privacy protections, including meeting passwords and waiting rooms, helping hosts better control participant access.

Slack

In 2019, a security researcher discovered a critical vulnerability in Slack's platform. This flaw allowed attackers to force users into fake session redirects, enabling the theft of session cookies. With these stolen cookies, attackers could gain unauthorized access to all data shared within a user’s Slack account, potentially compromising sensitive organizational information.

Slack’s security team responded swiftly, patching the vulnerability within 24 hours of its discovery, demonstrating the importance of rapid response to security threats.

GitLab

In 2017, a security researcher identified a severe vulnerability in GitLab’s session management. The platform exposed users’ session tokens directly in URLs and employed persistent tokens that never expired. This combination of open exposure and non-expiring tokens created a significant security risk. Attackers could obtain these tokens through various means, including brute force attacks, and use them indefinitely to access user accounts.

GitLab addressed this issue by revising its token usage and storage methods, emphasizing the critical nature of proper session token management in web applications.

While it’s true cybercriminals are developing more and more sophisticated methods of perpetrating these attacks, organizations can protect themselves by following these steps to detect and prevent session hijacking:

1. Use HTTPS and HSTS

Implementing HTTPS across an entire website encrypts all traffic between the user and server, making it extremely difficult for attackers to intercept session IDs. HTTP strict transport security (HSTS) forces browsers to always use HTTPS connections, preventing downgrade attacks. This encryption protects against packet sniffing and man-in-the-browser attacks, significantly reducing the risk of session hijacking.

2. Implement strong session management

Generate long, random, and complex session ID tokens using cryptographically secure methods. Couple these IDs with appropriate session expiration times and regenerate session IDs after significant events like successful authentication.

Validating the IP address of incoming requests against the session’s associated IP, terminating the session, or requiring additional authentication if there are sudden changes will add another layer of protection. These practices make it much harder for attackers to infiltrate systems by guessing or brute-forcing session IDs.

3. Enable HTTP-only and secure flags on cookies

Setting the “HTTP-only” flag prevents client-side scripts from accessing session cookies and protects against cross-site scripting attacks. The “secure” flag ensures cookies are only transmitted over HTTPS connections. These measures significantly reduce the risk of session cookie theft through common attack vectors.

4. Implement multifactor authentication (MFA)

MFA adds an extra layer of security by requiring additional authentication methods beyond just passwords. Even if an attacker manages to hijack a session, they would still need the second authentication factor to gain full access. This greatly enhances security, especially for sensitive operations or critical data.

5. Educate users and implement client-side protections

Teach users about the risks of public Wi-Fi, the importance of logging out after sessions, and how to recognize attack attempts. Encourage employees to use VPNs when they access the corporate system on public networks.

On the client side, implement features like automatic session timeouts and the option to view and terminate active sessions. These measures empower users to protect themselves and provide additional safeguards against session hijacking attempts.

Also, be sure to keep systems and software up to date, as updates patch many session hijacking vulnerabilities.

• Cross Site Scripting (XSS)
• Malware
• Web Application and API Protection (WAAP)
• Web Application Security

Session hijacking attacks can cause significant damage, but they can be stopped. With the right education and tools, organizations and individuals can keep their most precious data safe from the prying eyes of cybercriminals.

Of course, working with cybersecurity experts can help. Barracuda offers Web Application Protection that can keep users safe beyond a username and password. Contact our team today and try our Application Protection free to experience what it can do for you and your clients.