To stop credential stuffing on a store login, offer multi factor authentication, check new passwords against known breach lists, rate limit login attempts, and watch for unusual sign in patterns. No single control is enough, so layer them and notify customers of suspicious events.
What credential stuffing is
OWASP defines credential stuffing as the automated injection of stolen username and password pairs into website login forms to fraudulently gain access to accounts. It works because many people reuse passwords. OWASP calls it one of the most common techniques for account takeover and lists what attackers do next: drain stored value or make purchases, access card numbers and other private data, send phishing messages, or sell valid credentials.
It differs from brute force, which guesses passwords. Stuffing uses known pairs from other breaches. Password spraying tries one weak password against many accounts.
Why stores are a target
Store accounts hold saved addresses, order history, loyalty points, store credit and sometimes saved payment methods. Points and credit can be turned into goods quickly. The attacker does not need to break your systems, only to reuse leaked passwords.
Defenses, layered
OWASP's Credential Stuffing Prevention Cheat Sheet describes these.
| Control | What it does | Limit |
|---|---|---|
| Multi factor authentication | Blocks most password based attacks | Adds friction for users |
| Breached password checks | Rejects known leaked passwords at sign up and change | Does not stop already reused ones |
| CAPTCHA | Slows automated attempts | Can be bypassed by solving services |
| Rate limits and monitoring | Flags bursts of failed logins | Slow attacks can stay under limits |
| User notifications | Alerts customers to unusual events | Avoid overwhelming them |
The cheat sheet notes Microsoft analysis suggesting MFA would have stopped 99.9% of account compromises, and says adding another knowledge factor does not count as MFA.
Practical steps for a store
- Offer MFA, and make it the default for staff and admin accounts first.
- Check new passwords against a breached list.
- Track failed logins per account and per source, and alert on spikes.
- Protect points, credit and saved payment methods with a re-check before use.
- Email customers when a login comes from a new device or when contact details change.
- Log sign in events so you can answer which accounts were touched.
Do not forget the admin side
Staff accounts in your store admin matter most. A stuffed admin login is far worse than a stuffed customer one, so require MFA there before anything else.
Quick check
Is password complexity enough?
No. A complex password that was reused and leaked still works for the attacker.
Should I lock accounts after failed attempts?
Be careful, since lockouts can be abused to deny service to real customers. Prefer step up checks and monitoring.
Sources
Safeguard's API security scan and DAST can test login endpoints on systems you own, and the free scan is at gold.safeguard.sh/scan.
Last reviewed: 19 October 2026.
