There are many different types of session hijacking, including session fixation, man-in-the-middle attacks, and active session hijacking. In active session hijacking, an attacker takes over a live session by stealing the session ID while the victim is already logged in. This can be done through methods such as network sniffing or cross-site scripting. The goal of active session hijacking is to impersonate the user, gain access to sensitive data, bypass security controls, escalate privileges, or perform unauthorized transactions.
Description:
Active session hijacking is a tactic where an attacker takes control of a user’s ongoing, authenticated session. It is when threat actors obtain an active session ID or token through methods such as network sniffing, cross-site scripting, malware, or exploiting weak session management. Active session hijacking aims to impersonate the victim by exploiting their current session, creating a false sense of legitimacy and allowing the attacker to access sensitive data, bypass security controls, and perform actions as if they were the user.
How it Works:
Most web applications use a session ID (such as a token or a cookie) to maintain a user’s authenticated state. The attacker exploits how websites manage logged-in users by targeting the system used to identify and validate active sessions. There are passive and active attacks, the first being employing servers and browser exploits to gather data from client activity and the second utilizing phishing or malware to obtain the session token. The first step of hijacking is to acquire the session ID. There are several ways threat actors can get it.
Session Fixation
A tactic where an attacker forces a victim to use a session ID that the attacker already knows. This is an active attack. It is when threat actors create or obtain a valid session token in advance, often by embedding it in a malicious link or script and then trick the victim into logging in with that same identifier. Once the victim authenticates, the application ties the attacker’s chosen session ID to the victim’s account. Session fixation aims to let the attacker hijack the session after login, giving them the ability to impersonate the user, access sensitive information, and perform actions with the same privileges as the victim.
Man-in-the-Middle (MITM)
A tactic where an attacker secretly intercepts communication between a user and a server. This is a passive attack. It is when threat actors position themselves in the data stream, often through methods like ARP spoofing, DNS poisoning, or exploiting insecure Wi-Fi, to capture or even alter session cookies and authentication tokens. MitM session hijacking aims to impersonate the victim in real time, allowing the attacker not only to steal active sessions but also to manipulate transactions, inject malicious content, or gain ongoing access to sensitive systems under the guise of a legitimate user.
Phishing-Based
Attackers trick victims into handing over their active session details through a deceptive message or website. This is an active attack and is also known as cookie theft. It works by sending a phishing email or text that leads to a fake login page or a malicious proxy site. When the victim enters their credentials or logs in, the attacker’s site doesn’t just capture the username and password, it also grabs the session cookie or token that proves the victim is already authenticated. With that stolen token, the attacker can inject it into their own browser and instantly impersonate the victim, bypassing passwords and MFA protections, and carrying out actions as if they were the legitimate user.
Other Types
Other types of session hijacking include session sidejacking, where attackers capture session cookies by sniffing unencrypted traffic on open networks, and cross-site scripting, where malicious code is injected into trusted websites to steal tokens directly from a user’s browser.
Mitigations:
If a user is compromised, immediate mitigation should include terminating the affected session, changing passwords, and logging out of all active associated sessions. Mitigating session hijacking requires a multi-layered approach that secures authentication, strengthens session management, hardens cookies, and detects suspicious activity in real time. Since threat actors can use different delivery methods, such as phishing, smishing, man-in-the-middle attacks, or cross-site scripting, defenses must protect not only the communication channel but also the tokens themselves and the users targeted.
Phishing Awareness
A critical mitigation because so many session hijacking attacks begin with a smishing text or phishing email that tricks a user into clicking a malicious link. Even with strong technical defenses, a well-crafted lure can still get past filters. Regular training programs should teach employees how to recognize suspicious emails, texts, and login prompts, focusing on red flags like urgent language, mismatched URLs, or unexpected requests for authentication. Simulated phishing campaigns can reinforce this knowledge in a safe environment, helping users practice safe responses under realistic conditions. When paired with clear reporting channels for suspected phishing attempts, awareness programs reduce the likelihood that a victim ever clicks a malicious link in the first place, shutting down session hijacking attacks before they can begin.
Phishing-Resistant Authentication
This is one of the strongest defenses against session hijacking that begins with smishing or email phishing. Traditional MFA such as SMS codes can still be bypassed if an attacker captures the live session token, but phishing-resistant methods like FIDO2/WebAuthn keys, hardware tokens, or number-matching push notifications bind authentication to a device and make it far harder to replay sessions from another system. This ensures that even if a victim clicks a phishing link, the attacker cannot simply inject the stolen token into their own browser.
Session Token Binding
This is another critical mitigation that stops attackers from reusing stolen cookies. By tying tokens to a device fingerprint, IP address, or geolocation, organizations can ensure that a hijacked session cookie is valid only in the context of the original user’s environment. If the attacker attempts to replay that token on a different machine or location, the session is immediately invalidated, cutting off the attack before it can succeed.
Shortening Session Lifetimes
Enforcing idle timeouts and reducing session lifetime reduces the opportunity window for attackers. Cookies should be set to expire quickly, and inactive users should be logged out automatically, forcing re-authentication before sessions can be abused. For especially sensitive actions, such as initiating a wire transfer or changing account settings, applications should require fresh authentication, limiting the damage even if a session token is stolen.
Continuous Monitoring and Anomaly Detection
This provides the last line of defense against session hijacking. Security systems should watch for signs like concurrent logins from distant locations, impossible travel speeds, or sudden privilege escalations that indicate an account takeover in progress. Suspicious sessions can then be terminated automatically, with alerts sent to both the user and administrators for rapid response. Combined with security awareness training to help employees recognize smishing and phishing lures, monitoring ensures that even if an attacker succeeds in stealing a token, the compromise can be detected and contained quickly.