What is session hijacking?

Session hijackers can monitor browsing histories, search terms, financial information, and login credentials. They pose a significant cybersecurity threat to any organization.

How session hijacking works

Session hijacking exploits our reliance on sessions to establish web connections.

Users create web sessions whenever they access websites. Sites issue a session token or cookie which acts as a virtual handshake, approving the connection. Session tokens last for specific durations and authorize data transfers between visitors and websites.

This system allows website visitors to browse different pages on the same website without needing to authenticate their connection when moving between pages. Without sessions, navigating the web would be complicated by endless password requests.

However, convenience comes with a price. Attackers can intercept sessions, exposing every data packet we send over the public internet to malicious outsiders.

Stages in a session hijacking attack

A session hijacking attack generally has three stages: stealing IDs, establishing control, and weaponizing their position of power.

Stealing the session ID

Session hijacking starts by stealing the session ID stored in tokens or session cookies. The session ID identifies the user and their session state, making it possible to impersonate the target and browse websites on their behalf.

Attackers use various techniques to steal session credentials. The simplest method involves brute-forcing. In brute-forcing attacks, criminals keep guessing session IDs based on previous IDs from the same website. If the website owner relies on a generic ID format, attackers may eventually succeed.

If brute-forcing fails, session hijackers may try packet sniffing session cookies, installing Trojans to steal data, or launching scripting attacks. The result is always the same: criminals seize control of sessions without the users' knowledge.

Taking over the session

The next step is assuming control of the user's session. Attackers with the session ID can send that ID to the web server. The server approves their connection, believing the attacker is the original user. Attackers then gain access to the website or platform and can take actions disguised as their victim.

Criminal activity

After gaining control of a web session, criminals can harm their targets in several ways. They could leverage the user's privileges to access corporate databases and extract customer data. They could exfiltrate confidential intellectual property, arrange financial transfers, or maliciously disrupt network activity.

Why carry out session hijacking attacks?

Session hijacking appeals to cybercriminals because the benefits are potentially vast. When they obtain the session token or cookie, attackers can take over an ongoing session—harvesting data and even issuing commands on behalf of the user.

Session hijacking is also relatively simple. Criminals do not need to obtain passwords or other credentials. Session hijacking attacks provide access to platforms and sites quickly and—in many cases—with a lower detection risk.

Another benefit of hijacking active web sessions is that it allows attackers to bypass multi-factor authentication and single sign-on portals.

Types of session hijacking

Security teams must understand how session hijacking takes place before implementing effective countermeasures.

Common session hijacking attack methods include:

• Cross-site scripting (XSS). These session hijacking attacks inject malicious code into compromised online forms. In some cases, they can re-engineer websites to extract the session keys of site visitors.
• Session sniffing. Also known as session-side jacking, session sniffing tends to follow man-in-the-middle interception attacks as it relies on access to the target's network traffic. When attackers gain access, they can "sniff" data packets to detect session IDs and use these IDs to hijack web connections.
• Session fixation. In fixation attacks, cybercriminals persuade targets to start sessions with compromised session cookies. Attackers typically start session fixation attacks via phishing emails containing links to malicious websites. When users log into these fake sites, attackers can take control of their browser session.
• Man-in-the-browser attacks (MITB). MITB attacks are like man-in-the-middle attacks, but limited to web browser users. Attackers infect targets with Trojan malware which spreads to their browser. This malware can then issue instructions to websites (such as financial withdrawals). As these requests originate from user devices, websites often authorize them—allowing criminals to benefit.
• Guessing predictable session IDs. This session hijacking method exploits the algorithms used by a web server to generate session IDs. Many servers create patterns as they distribute IDs. Criminals can learn these patterns and guess session IDs—a faster form of brute-force session hijacking attack.
• HTTP interception. Some websites remain undefended by TLS encryption. This makes every visitor vulnerable to session hijacking. Snoopers can intercept traffic and assume control without decrypting session ID information.

Session hijacking case studies

The categories above are general guides. In the real world, session hijacks take many forms, often including different strategies. Let's explore a few real-life cyberthreats scenarios that show how criminals apply hijacking techniques.

Zoom

Session hijackers briefly made headlines in 2020 and 2021 by crashing Zoom sessions worldwide. The video communication platform expanded rapidly during the pandemic, but security measures did not evolve in step.

"Zoom Bombers" found ways to brute force and guess meeting IDs. In some instances they took control of group discussions, making communication impossible.

CVS medical data

Healthcare retail giant CVS experienced a session hijacking attack in 2021, leaking over 1 billion patient records. Eventually, investigators found that misconfigured databases allowed session hijackers unauthorized access. Attackers gained access to cloud user logs, prescriptions metadata, and private medical queries.

CircleCI

DevOps platform CircleCI announced a session hijack in 2023. In this case, attackers used stolen GitHub OAuth session cookies to implant infostealer malware.

Threat actors did not need to breach CircleCI's two-factor authentication. They exploited weaknesses in GitHub tokens and escalated their privileges to obtain unauthorized access to admin-level accounts. As a result, attackers gained access to all corporate DevOps accounts—including valuable IP and ongoing projects.

How to detect session hijacking

Companies that regularly experience session hijacking attacks will eventually feel the consequences via data breaches, malware infections, and denial-of-service attacks. Effective detection measures are essential parts of any security setup.

Security teams should focus on detecting session anomalies. For example, session lengths may fluctuate more than normal. Sessions may remain open outside office hours or when employees are not active.

Consult user logs to define baseline behavior for legitimate users. Use these baselines as reference points when assessing patterns in resource usage, connection duration, and network activity.

Multiple sessions from different IP addresses simultaneously can indicate hijacking attacks. IP addresses may suddenly change mid-session without users engaging a VPN or changing their state in other ways.

Session fingerprinting also helps identify potential hijacks. Fingerprinting tools can detect device, operating system, and browser information at the start and end of sessions. Mis-matches often signify malicious activity.

It's also advisable to use threat detection tools to automate basic hijacking alerts. For instance, tools should alert security teams when users gain access to resources following repeated failures. Re-using a session ID or sudden activity spikes should also generate alerts for investigation.

Together, the recommendations above help identify session token misuse. To be effective, they require a proactive security policy that constantly investigates alerts and audits user activity. Any unusual patterns should prompt action, as they could be evidence of compromised session tokens.

How to prevent session hijacking attacks

Detection is half the challenge. Organizations should also take action to prevent session hijacking before incidents occur. Complete prevention may not be possible (investment in detection is critical), but the steps below will cut the risk posed by hijacked session cookies:

• Require VPN usage. Virtual Private Networks encrypt network traffic and conceal your browsing activity from outsiders. Session hijackers rely on visibility to track users and obtain session token data. VPNs make targets far less attractive and—sometimes—impossible to detect.
• Don't use unsecured public Wi-Fi. Criminals prey on unsecured Wi-Fi networks without encryption or proper authentication systems. Employees should avoid using public Wi-Fi to send work-related data. If they need to work in public, make VPNs mandatory.
• Educate staff to avoid phishing emails. Remember that many session fixation hijacks start by clicking a malicious link. Train employees to identify suspicious emails and websites and refresh staff knowledge annually to maintain high awareness levels.
• Use allowlisting to control web usage. Many firewalls include allowlisting tools. These tools maintain lists of approved websites. generally sites essential for business tasks. They help divert employees from dangerous browsing and reduce the attack surface available to hijackers.
• Always avoid unencrypted websites. Employees should never visit sites lacking the S after "HTTP" as these sites are insecure. Use reliable threat detection software that draws on threat intelligence to identify malicious websites.
• Strengthen your malware protection. Some session hijacking attacks start with Trojan malware. Ensure you have cutting-edge malware and virus detection tools.
• Use secure coding practices. Audit web forms and website code to remove exploits or scripting vulnerabilities. Additionally, make sure you apply session management for all web apps or services.

Most importantly, companies should be vigilant and proactive when countering session hijackers. Organizations may become complacent, believing their existing network security measures are sufficient.

Remember that session hijacking bypasses two and multi-factor authentication systems, as well as access management systems like Azure. Users may not know they are victims of hijacks, and detection requires careful threat monitoring.