Account Takeover & Credential Stuffing
One-line relationship: the large-scale, automated cousin of phishing — reusing credentials breached from other sites rather than harvesting them fresh — and the clearest case for why passkeys and bot management are complementary, not redundant.
What it is
Credential stuffing is the automated attempt of username/password pairs — harvested from an unrelated breach — against a login endpoint at scale, betting on password reuse across sites. It doesn’t require breaking anything about the target site; it only requires that some fraction of users reused a password that leaked elsewhere. Account Takeover (ATO) is the outcome: an attacker gains control of a legitimate account through stuffing, phishing, or any other credential-compromise route, then operates it as if they were the genuine user.
Why passkeys blunt this structurally
Credential stuffing only works because passwords are shared secrets that can be typed anywhere and are frequently reused. A passkey has no password-equivalent to breach in the first place — there’s nothing sitting in some other company’s database that an attacker can replay here, because the private key never left the user’s authenticator and was never transmitted or stored server-side in a reusable form. Moving from passwords to passkeys doesn’t just make credential stuffing harder, it removes the input the attack needs entirely.
Why bot management still matters
Passkey adoption is gradual — as long as any password-based login path exists (a legacy fallback, a lower-assurance flow, a partner integration), credential stuffing against it remains viable, and it’s fundamentally a volume attack: millions of attempts, scripted, from rotating infrastructure. That’s precisely what bot management / anti-automation (C5) is built to catch — distinguishing scripted, high-velocity traffic from genuine human logins — independent of whether the credentials being tried are individually valid. Rate limiting and velocity controls are the blunt instrument version of the same idea.
What to take to the client
Credential stuffing is a numbers game that doesn’t care how strong any individual password is — it only needs reuse. Passkeys close the structural gap; bot management and rate limiting are what protect whatever password-based surface remains during the transition, and remain relevant defense-in-depth even after passkeys are the default, for any endpoint an automated attacker might still probe.