Credential Stuffing
Credential stuffing attacks exploit the common practice of password reuse. When users reuse the same passwords across different platforms, a single data breach can compromise accounts on multiple services.
What is credential stuffing
Credential stuffing is a type of cyberattack where attackers use automated tools to test large volumes of stolen username-password pairs across multiple websites and applications. Unlike brute force attacks, which attempt to guess passwords, credential stuffing relies on passwords that have already been compromised in previous data breaches.
The attack works because many users reuse the same passwords across multiple services. When a data breach occurs at one service, attackers obtain username-password pairs that may work on other platforms where users have created accounts with the same credentials.
Attackers typically obtain these credential lists from data breaches, dark web marketplaces, or credential dumps. They then use specialized tools and bots to automate login attempts, making thousands of requests per minute across multiple targets. To avoid detection, attackers distribute requests across multiple IP addresses, use proxy networks, and rotate user agents to mimic legitimate traffic patterns.
How credential stuffing differs from brute force attacks
While both attack methods target authentication systems, they differ in important ways. Credential stuffing uses stolen, real credentials from data breaches, while brute force attacks attempt to guess passwords through trial and error. Credential stuffing is typically faster and more successful because it uses real credentials, whereas brute force attacks rely on probability and can take much longer. Credential stuffing attacks can also be more difficult to detect because they use legitimate-looking credentials, while brute force attacks often show clear patterns of failed attempts.
Preventing credential stuffing
Organizations can implement multiple layers of defense to protect against credential stuffing. Rate limiting restricts the number of login attempts from a single IP address or user account within a specific time period, making automated attacks more difficult and slower to execute.
Bot detection systems identify automated login attempts by analyzing behavioral patterns, such as mouse movements, typing cadence, and request timing. Advanced bot detection can distinguish between legitimate users and automated scripts.
Multi-factor authentication (MFA) adds an additional layer of security beyond passwords. Even if attackers obtain valid credentials, they cannot access accounts without the second authentication factor.
Other prevention strategies include implementing CAPTCHA challenges, encouraging users to create unique passwords for each service, monitoring login attempts for suspicious patterns, and checking user passwords against known breach databases during registration or password changes.
Credential stuffing protection in Clerk
Clerk provides multiple security features to help protect applications against credential stuffing attacks. Clerk's authentication system includes advanced bot detection capabilities that identify and block automated login attempts. Clerk also implements rate limiting on authentication endpoints to prevent rapid-fire credential testing. Clerk also supports multiple MFA methods, including TOTP, SMS, and email-based authentication, adding layers of protection beyond passwords.
Most importantly, Clerk includes Client Trust, which automatically requires a second factor for new devices, even if the password is valid.
Developers can also implement additional security measures, such as IP allowlisting, device fingerprinting, and custom rate limiting rules, to further protect against credential stuffing attacks.