Credential Stuffing.
An automated attack that replays username-password pairs harvested from data breaches against unrelated sites, exploiting password reuse.
Credential stuffing volume against major SaaS targets runs in the millions of attempts per day. Most are filtered at the network layer (Cloudflare bot management, Akamai Bot Manager, DataDome). The residual hits the auth layer where breached-password detection and rate limiting take over. The single highest-leverage long-term defense is passkey adoption, the attack class doesn't apply to credentials that aren't reusable across sites.
Common questions
How is credential stuffing different from brute force?
Does MFA stop credential stuffing?
Can passkeys eliminate credential stuffing?
Related terms
In the guides
Account Takeover Defense: A Layered Approach for 2026
ATO is the single largest CIAM threat in 2026. The defense stack is layered, credential stuffing protection, MFA, session management, and recovery design, each addressing a different attack class.
Password Security and Storage: Hashing, Salting, and What Actually Works in 2026
Passwords still exist, and storing them correctly still matters. The 2026 production-grade answer: Argon2id with per-user salt, optional pepper, no fast hashes, no reversible encryption.