What is Credential Stuffing?

Credential stuffing is an attack in which bots try out username and password pairs stolen from one service on many other websites. Since many people reuse passwords, attackers "stuff" these credentials into login forms hoping to find a match. A successful credential stuffing attack can give attackers access to user accounts on the targeted site, leading to data breaches or account misuse.

How Credential Stuffing Works

The credential stuffing process typically follows these steps:

1. Data acquisition: Attackers obtain credentials from data breaches, either through direct involvement in breaches or by purchasing stolen credentials on dark web marketplaces

2. Preparation: Attackers format the stolen credentials and set up automated tools to test them across multiple websites

3. Automated testing: Bots systematically attempt login with each username and password combination on target websites

4. Success validation: When a login succeeds, the working credentials are flagged for use in further attacks

5. Account exploitation: Successful logins lead to account takeovers, which can result in data theft, fraud, or identity theft

Why Credential Stuffing Works

Credential stuffing is effective because:

• Password reuse: Studies show that 65% of people reuse the same password across multiple sites
• Database breaches: Billions of credentials have been exposed in major data breaches
• Automation efficiency: Bots can test thousands of credentials per minute
• Scale advantages: Even a low success rate (typically 0.1-2%) yields significant results when millions of credentials are tested

Detection Signs

Organizations can identify potential credential stuffing attacks by watching for:

• Abnormal login patterns or volumes
• Multiple failed login attempts from the same IP address
• Login attempts from unusual geographic locations
• Logins using outdated browser versions (often used by bots)
• Higher than normal login failure rates

Protection Measures

Effective protection against credential stuffing includes:

• Rate limiting: Restricting the number of login attempts from a single source
• CAPTCHA challenges: Requiring human verification after suspicious activity
• Multi-factor authentication (MFA): Adding a second verification step that stolen passwords alone cannot satisfy
• IP reputation checking: Blocking login attempts from known malicious IP addresses
• Advanced bot protection: Implementing solutions that can identify and block automated login attempts
• Device fingerprinting: Identifying suspicious devices or browser configurations

Impact on Businesses

Credential stuffing attacks can cause significant damage:

• Account takeovers: Leading to fraud and unauthorized transactions
• Customer data breaches: Exposing sensitive personal information
• Compliance violations: Potentially triggering regulatory penalties
• Loss of customer trust: Damaging brand reputation
• Service disruption: Consuming system resources or triggering security lockdowns

Implementing robust bot protection is one of the most effective ways to prevent credential stuffing attacks, as it stops automated testing before stolen credentials can be validated.