What session hijacking is
Session hijacking is an attack in which someone takes over a user's active session on a website or service. When a user logs in, the site typically maintains a session that identifies them, often using a session identifier such as a token. If an attacker obtains that identifier, they can use it to impersonate the user, effectively taking over the session without needing the user's password.
The role of the session identifier
After a user authenticates, the site needs a way to remember who they are across requests. It does this with a session identifier, a piece of data that stands in for the user's logged-in status. Possessing this identifier is like holding a key to the session. That is why it is so sensitive: whoever has it can act as the logged-in user.
How attackers take over a session
To hijack a session, an attacker tries to obtain a valid session identifier. There are various ways this might happen, such as intercepting it as it travels or acquiring it through other weaknesses. Once the attacker has the identifier, they can present it to the site, which then treats their requests as coming from the legitimate user, granting them the user's access.
Why it is dangerous
Session hijacking is dangerous because it lets an attacker act with the full privileges of the victim's session, without the victim's knowledge. The attacker does not need the user's credentials, only their session identifier. This can give access to the user's account and data for as long as the session remains valid, making it a serious threat to users' security.
Preventing session hijacking
Defenses against session hijacking focus on protecting the session identifier so that attackers cannot obtain it. Measures such as encrypting the connection so the identifier cannot be intercepted, and handling sessions carefully, help keep the identifier secret. By safeguarding this key piece of data, sites reduce the chance that an attacker can steal and reuse a user's session.
Why it matters
Session hijacking is an important web security concept to understand. Knowing what it is - taking over a user's session, often by stealing its identifier - clarifies why protecting session data is essential. For anyone interested in web security, it is a valuable concept to understand.
Related on Skillo
See also: What is a cookie? Explained, What is two-factor authentication (2FA)?.
Sources
Published date reflects the original event date (2026-05-26). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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