What is session hijacking, and how can you prevent it?

A session is the time a user spends interacting with a website or app after logging in. During this time, the system uses a unique session ID to track the user’s activity. This ID allows the user to stay logged in without having to enter their details again for every action. The session starts when the user logs in and continues until they log out or remain inactive for some time. Session hijacking occurs when an attacker steals the user's session ID, allowing them to impersonate the user and access sensitive data or perform actions as if they were the legitimate user. In this article, we’ll explain how this cyberattack works and provide tips on how to prevent session hijacking.

What is session hijacking?

Session hijacking is a cyberattack in which an attacker takes over the user’s active sessions on a website or application by stealing or intercepting the unique user’s session ID. This session ID is an identifier stored in a user’s cookies that validates their logged-in status. Because of this, session hijacking can also be called cookie hijacking.

Session hijacking allows attackers to bypass traditional login processes, enabling unauthorized access without needing the user’s credentials. Once the attacker has the session ID, they can impersonate the user online. By acquiring the web session ID, the attacker can impersonate the user online. This way, the hacker appears on the network as if they were a legitimate user, which allows them to gain access to private information or carry out actions in the victim’s account.

Session hijacking often targets web applications and relies on vulnerabilities in network security or session management. Attackers use methods like network eavesdropping, cross-site scripting (XSS), or packet sniffing to execute the attack. One common form of this attack is TCP session hijacking, where the attacker intercepts and manipulates the network traffic (or transmission control protocol) between a user and a server, allowing them to control the connection.

Session hijacking poses serious risks, especially for those using online shopping, banking, or accessing corporate data. By hijacking a session, attackers gain the same access as the legitimate user, which can lead to various consequences, including a data breach, identity theft, or financial loss. Since many applications use session IDs as a primary means of validation, a compromised session ID can be as damaging as a stolen password.

How does session hijacking work?

A session hijacking attack typically unfolds in several stages, starting with the user logging in to a website as usual:

Step 1: The user logs in to an account as usual. The user accesses an online service, such as a banking app, shopping site, or social media platform. Upon logging in, the server assigns a unique session ID to the user’s session and places it in a session cookie in their browser. This cookie tracks their session and allows them to stay authenticated while they browse or perform actions on the site. Sessions remain active until the user logs out or is inactive for a certain period of time.

Step 2: An attacker then intercepts the session. Cybercriminals use various methods to access this active session. They might employ packet sniffing on unencrypted connections, session sniffing, cross-site scripting (XSS) attacks to steal session IDs, or man-in-the-middle (MitM) attacks to intercept session data. The attacker locates the user’s session ID, often within the cookie, and captures it to take over the session and impersonate the user.

Step 3: The attacker takes over the session. Once the attacker has the valid user’s session ID, they can use it to log in to the site as a legitimate user. With access to the session, the attacker can view sensitive information, make purchases, transfer funds, or perform other actions without detection because they appear authenticated to the server.

What methods are used to execute session hijacking?

Session hijacking is carried out using a variety of techniques, each exploiting different security gaps in online applications. Here are some of the most common methods attackers use to hijack sessions:

• Session fixation. An attacker assigns a predetermined session ID to a user before they log in. The attacker sends the victim a link or URL containing this session ID, often via phishing. Once the user logs in, the attacker can use the same session ID to access the account.
• Packet sniffing. Often used on unsecured networks (like public Wi-Fi), packet sniffing tools allow attackers to retrieve session IDs and take control of the session.
• Cross-site scripting (XSS). During cross-site scripting attacks, hackers inject malicious scripts into a website to steal session IDs from users who interact with the site. When a user clicks on a link containing the script, it executes in their browser, copying their session ID and sending it back to the attacker.
• Man-in-the-middle (MitM) attack. In a MitM attack, the attacker intercepts the communication between the user and the web server, potentially capturing session data like session IDs or login credentials. This method is often carried out on unencrypted or vulnerable networks.
• Session replay. The attacker captures and reuses a previously valid session ID to gain unauthorized access. If the server doesn’t validate session timing correctly, attackers can use these expired session IDs to take over user accounts.
• Session sidejacking (or session sniffing). Session sniffing is similar to packet sniffing but often targets encrypted HTTPS sessions. Attackers use packet sniffers to capture session IDs from network traffic, allowing them to impersonate the user.
• Man-in-the-browser attack. This type of attack is similar to a man-in-the-middle attack but involves malware installed on the victim's device. The malware waits for the victim to visit a targeted site and can then secretly alter transaction details or initiate additional transactions, making them appear as if they came from the victim’s device. This type of attack is hard to detect because it operates invisibly while the victim interacts with the website.
• Predictable session token ID. Some websites use weak algorithms to generate session tokens. If attackers can predict the session token pattern, they can create a valid session ID and gain unauthorized access.

How dangerous are session hijacking attacks?

Session hijacking attacks are highly dangerous for both individuals and businesses due to the attacker’s ability to impersonate the user and access sensitive information, leading to potentially severe financial, operational, and reputational damage.

For individuals, session hijacking can lead to identity theft and financial loss. Once attackers gain access to a user’s session, they can make unauthorized transactions, transfer funds from bank accounts, and use stored payment information to make purchases. Attackers might also steal personally identifiable information (PII), leading to long-term privacy breaches and increased vulnerability to further attacks. The ability to access private communication or data can cause lasting harm because cybercriminals use stolen information for fraud or malicious purposes.

Businesses face even greater consequences. When attackers hijack sessions within a corporate context, they can access sensitive company data, such as customer records, financial information, and proprietary software, leading to data breaches, financial loss from unauthorized transactions, and operational disruption. In addition, businesses might face compliance challenges under regulations like the GDPR or HIPAA, and if customer data is compromised, the company risks losing customer trust. Reputational damage can lead to decreased loyalty, lost revenue, and even legal action or regulatory fines if data protection standards are not met.

Attackers aim to get as much as they can from session hijacking. Beyond just stealing funds or personal information, attackers might use the hijacked session to install malware, allowing them to control the victim’s device or network, monitor activity, and steal additional data over time. The goal is to make the most of the compromised session, whether by stealing money, accessing private data, installing malware, or using the session to launch further attacks on other systems.

Real-life examples of session hijacking attacks

Session hijacking has impacted numerous companies and platforms over the years. Let’s take a look at some of the most notable cases in recent years.

Okta

In 2023, Okta, the identity and access management (IAM) vendor, experienced a breach in its customer support case management system that allowed a threat actor to hijack its customers' sessions. The breach originated from the compromised Google account of an employee, which stored credentials for a service account used to access support cases. Among the accessed files were HAR files containing session tokens that attackers then used to hijack sessions. The breach affected 134 customers, which is less than 1% of Okta's client base. Okta addressed the issue by improving its security measures and logging systems to prevent similar issues in the future.

Slack

In 2019, a vulnerability was discovered in Slack that allowed attackers to hijack sessions by redirecting users to malicious links. These links would steal session cookies, giving the attackers unauthorized access to private communications and data. This breach posed a severe risk for organizations relying on Slack for internal communication. Slack quickly patched the vulnerability within 24 hours after it was discovered, ensuring users' session details remained secure.

GitLab

GitLab, a platform used for code hosting and version control, was found to have a severe session-hijacking vulnerability. Session tokens were exposed in URLs, and these tokens were persistent, never expiring, allowing attackers to hijack user sessions even after extended periods. This vulnerability opened GitLab users to attacks because attackers could use brute-force methods to steal session tokens. GitLab resolved this issue by changing its session management practices and making tokens secure and time-bound.

How to prevent session hijacking attacks

The best protection against session hijacking is prevention. By implementing strong session hijacking prevention and security measures, you can significantly reduce the risk of attackers gaining unauthorized access to your sessions:

• Avoid public Wi-Fi. Cybercriminals use packet sniffing to intercept session data on public Wi-Fi networks, making them a common target. Avoid doing important tasks like online banking, shopping, or logging in to private user accounts while connected to public Wi-Fi.
• Use a VPN. If you must use public Wi-Fi, a virtual private network (VPN) creates a secure "private tunnel" for your online activity. It encrypts your connection and shields your session from attackers trying to intercept your data.
• Keep your software updated. Ensure all your apps and software are up to date, including security tools. Regular updates help protect your devices from vulnerabilities that attackers could exploit, including the malware used in session hijacking. Keeping your apps updated ensures you have the latest security patches and features to stay protected.
• Be cautious of phishing attempts. Avoid clicking on links in unsolicited emails, because they may lead to fake login pages or malware downloads. Always verify the sender’s legitimacy before clicking.
• Verify website security. Only use websites with "https://" and a padlock icon for sensitive transactions. This encryption ensures your data is encrypted and secure from interception.
• Use multi-factor authentication (MFA). MFA adds an extra layer of security, making it harder for attackers to hijack your session even if they steal your session ID.
• Use advanced security solutions. Protect your brand from stolen session cookies with NordStellar's session hijacking prevention solution. This tool scans the deep and dark web for stolen session cookies associated with your organization’s employees and customers. It detects info stealer malware infection, plus identifies IDs and cookies from compromised active sessions.