Browser-session hijacking is the takeover of an already authenticated web session by stealing or abusing session material stored in the browser. Instead of cracking a password, an attacker may capture session cookies, tokens, browser memory, or local storage and reuse them to impersonate the victim. Because the session is already trusted by the website, the attacker can often access accounts without triggering a fresh login prompt.
This matters in cyber security because modern defenses rely heavily on session state, not just credentials. If a token is stolen, multi-factor authentication may be bypassed for the active session, and the attacker can act as the user until the session expires or is revoked. In real intrusions, malware may target browser processes, cookie stores, or memory, then replay the stolen session from another system. Defenders look for unusual token use, suspicious browser access, impossible travel, and abnormal process behavior, and reduce risk with short-lived sessions, device binding, hardened browsers, and strong endpoint monitoring.