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Credential stuffing is an automated attempt to sign in to accounts using username-and-password pairs exposed elsewhere. If you reuse a password, a breach at one service can put your accounts on other services at risk. Use a different password for every account and turn on multi-factor authentication (MFA) wherever it is available.
How credential stuffing works
An attacker obtains username-and-password pairs from a data breach, phishing, or a credential dump, then uses automated software to submit those known pairs to other services’ login forms. A reused pair may work if the same credentials are still valid on another account. A strong password does not protect an account if that password was exposed and reused.
A successful login can expose personal information, private messages, documents, or payment data. Depending on the account, an attacker may also make purchases or send spam and phishing messages in the account holder’s name.
How credential stuffing differs from other password attacks
| Attack | What the attacker tries |
|---|---|
| Credential stuffing | Previously obtained username-and-password pairs, tested against other services. |
| Brute force | Many possible passwords against an account. |
| Password spraying | A small set of common passwords against many accounts. |
These methods can have similar consequences, but they are not interchangeable: credential stuffing depends on exposed credentials, while brute force and password spraying try possible passwords.
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How to protect your accounts
Use a unique password for every service
Unique passwords prevent a password exposed at one service from serving as a ready-made login attempt elsewhere. A password manager can help generate and keep track of different passwords; it is a convenience, not a prerequisite.
Turn on multi-factor authentication
MFA requires another factor in addition to your password. That can stop someone who has only the password from signing in. Enable it wherever offered, prioritizing email, financial, and other high-impact accounts. The FTC advises that when text or email codes are the only available option, using one is better than having no second factor: FTC guidance on two-factor authentication.
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A FIDO2 security key is one optional physical MFA method, but whether a key works depends on the service and your devices. Check the service’s supported sign-in methods before choosing one.
What to do if your credentials may have been exposed
- Change the password on the affected service. Choose a new password that you do not use anywhere else.
- Change that password on every other account where you reused it. Give each account its own password.
- Enable MFA on those accounts if the service offers it.
- Review the provider’s account activity and recovery settings for changes or activity you do not recognize. Use the affected provider’s account-security page for its specific controls.
How services defend against credential stuffing
Services can layer MFA with monitoring, automated-login detection, and risk-based step-up checks. Signals such as an unfamiliar device or location, or login activity that looks scripted, can prompt additional checks. OWASP recommends layered defenses because client-side measures such as device fingerprinting and JavaScript challenges can be spoofed or bypassed; CAPTCHA may slow or identify some automated attempts, but is not a complete defense. See OWASP’s credential-stuffing prevention guidance.
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CISA likewise explains that MFA can prevent account takeover when an attacker has a reused password but lacks the second factor. Its administrator guidance on credential cracking discusses credential stuffing and related threats.
Quick Recap
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