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Unauthorized reuse of a valid session identifier.

Definition

Session hijacking involves capturing or obtaining session identifiers (cookies/tokens) via XSS, network interception, malware, or phishing, then replaying them to impersonate the user.

In plain English Unauthorized reuse of a valid session identifier.

Why this matters

Why it matters: It enables account access without needing the user’s credentials once a session token is obtained.

Example

Example: Token theft via XSS followed by replay from a different device.