Credential stuffing reuses passwords. Session theft reuses an already approved login.

Credential stuffing

Attackers test username-and-password pairs obtained elsewhere against another service. The attack relies on password reuse and automation, not a new breach of the target service. Rate controls, breached-credential screening, strong MFA, password managers, and useful login monitoring can reduce success.

Session theft

A session token tells a service that authentication already happened. Malware, browser compromise, exposed logs, or other access can let an attacker reuse that session without entering the password again. A password change may not end the session unless the service revokes it.

Read the sequence

Investigators should compare login method, device and network context, token issuance, session age, recovery changes, and actions after access. A new device after repeated failed logins suggests a different path from a familiar session that suddenly changes payees. Signals guide investigation; they do not replace evidence.

Look for the account changes that persist

After restoring access, review recovery addresses, authenticators, API keys, delegated applications and high-consequence actions. Preserve the timeline and distinguish activity the account holder confirms from activity the evidence only suggests. Device or location changes are signals, not proof; the complete sequence supports the decision.

Example: two attacks create similar account activity

Credential stuffing may produce many failed logins followed by a success from reused credentials. Session theft may begin with a valid session and no new password event. Both can lead to profile changes or purchases, but the telemetry and containment differ. A review should avoid assuming the access method from the fraud outcome alone.

Reduce reusable access at both layers

Unique passwords and phishing-resistant authentication reduce credential reuse. Short-lived, revocable sessions, secure token handling and visible device controls reduce the consequence of session theft. Neither layer replaces endpoint security or recovery review. The account lifecycle needs to remove old sessions and delegated access when trust changes.