What is a Session Hijacking Attack and How to Prevent It

What is session hijacking?

Session hijacking is a cyberattack in which an attacker steals or manipulates a valid session identifier (also called a session token or session ID) to impersonate an authenticated user. Once a session is hijacked, the attacker may gain access to accounts, personal information, financial services, or business systems without needing the user's password. A session lasts for as long as the connection remains between the two endpoints and is defined by a session ID.

Session hijacking means one of these sessions is taken over (usually by a hacker or virus) by pretending to be an authorized user. To hijack a session, the attacker must discover the session ID which can be used to masquerade as the authorized user.

How session hijacking works

Session hijacking is when an attacker convinces a server or website that they are an authorized user. There are several session hijacking types, but they generally go something like this:

1. An authorized user logs into an online account (for example, their bank account). The site then loads a “session cookie” in the user’s browser. This contains the user’s session ID which keeps the user authenticated and enables them to interact with the website like normal.
2. While the user is connected to the site, an attacker steals their session ID. They then use this session ID to sign themselves into the website as the authenticated user without being detected.
3. The attacker can then steal money from the user’s bank account. On other sites, an attacker might be able to purchase something, steal their identity, or steal and encrypt data for a ransom.

Many users assume that passwords are the primary target in account attacks. However, session hijacking often targets the authenticated session itself. After a user successfully signs in, the website uses a session token to recognize them during future interactions. If an attacker obtains that token, they may be able to bypass the login process entirely and operate with the same permissions as the legitimate user.

Types of session hijacking

There are two main categories of session hijacking: Active session hijacking and passive session hijacking. In real-world attacks, active and passive session hijacking techniques are not always separate. An attacker may first passively collect information about a target before actively taking over the session. Modern cyberattacks frequently combine multiple techniques to increase the likelihood of success.

Active session hijacking

Active session hijacking is when an attacker actively takes over a user’s session by forcing them offline and preventing them from communicating with the server. The attacker can then perform any action they like, such as stealing money from a bank account.

Passive session hijacking

Passive session hijacking is when an attacker simply monitors traffic between a user and a server. This lets them discover passwords or other valuable information they can use to masquerade as the user or ransom their personal information.

Session hijacking techniques

Modern websites often use additional protections to reduce the risk of cookie theft. Security mechanisms such as Secure cookies, HttpOnly cookies, and SameSite cookie settings help limit how session data can be accessed and transmitted. While these controls improve security, they do not completely eliminate the risk posed by vulnerable websites or compromised devices.

There are several different types of session hijacking, including:

• Session-side jacking. Session-side jacking or cookie sniffing involves using an application or proxy to steal network traffic between a website and the user. This contains the session ID token that can be used to masquerade as the authorized user.
• Cross-site scripting. This is when an attacker makes use of weaknesses in a website’s security to inject their own malicious links. When a user clicks those links, cross-site scripts activate which allow the attacker to see your session ID. This is one reason why it’s a good idea to disable cross-site tracking.
• Brute force. Brute force attacks involve an attacker guessing your session ID to hijack the session. Often, session IDs are created by algorithms. If an attacker can find several session IDs, they may be able to determine the algorithm and predict a usable session ID.
• Session fixation. This is when the attacker creates a session ID and convinces the authorized user to start a session with it. For example, the attacker might send them a fake email with a link to a login form. When the user logs in using that session ID, the attacker then has access.
• Malware injection. Attackers often try to trick users into installing malware which will monitor their activity and steal their data. This malware is able to find and steal your session ID so that the attacker can hijack your session.

Some session hijacking attacks rely on malware or spyware running silently on a victim's device. These threats can monitor activity, collect sensitive information, or attempt to steal session data used to keep accounts authenticated.

Clario Anti Spy's Hidden app scan helps identify suspicious apps, spyware, and other potentially unwanted software that may be secretly installed on your iPhone or Android device. The scan also reviews app permissions, making it easier to spot software requesting access that may not be necessary for its stated purpose.

How to find hidden apps with Clario Anti Spy’s Hidden app scan:

1. Download Clario Anti Spy and set up a subscription.
2. Under Hidden app scan, tap Scan.

How to prevent session hijacking

There are several things you can do to prevent session hijacking and protect your data and identity online, including:

• Use a VPN. A high-quality VPN can mask your IP address and keep your online activity private and secure.
• Avoid public or unsecure Wi-Fi networks. Because public Wi-Fi requires no authentication to connect, a hacker is able to position themselves between you and the connection point. This enables them to monitor and steal your information.
• Avoid scams. The main way you can avoid scams is by never clicking on a link in an email unless you’re sure it’s from a trusted source.
• Use security software. Security software like a high-quality antivirus can act as a last line of defense between you and malicious actors online. If you accidentally click a link, it might be the only thing that prevents malware from being installed.
• Make sure you only connect to secure sites. Older sites and small sites run by owners who aren’t very security savvy will often have several security loopholes. For this reason, it’s important to only load sites from reputable, trusted companies. The most secure sites now use HTTPS (rather than the older HTTP), so keep an eye out for this in your address bar.

Final thoughts

Session hijacking remains a serious threat because attackers can abuse active sessions to access accounts without repeatedly entering credentials. While practicing safe browsing habits, avoiding suspicious links, and using secure websites can reduce your risk, hidden spyware may still expose sensitive session data. Clario Anti Spy's Hidden app scan helps identify suspicious apps, spyware, and risky permissions on iPhone and Android devices, adding an extra layer of protection for your privacy and online accounts.