Credential Stuffing: What It Is, How It Works and 7 Ways to Prevent It

What is credential stuffing? 

Credential stuffing is a cyberattack using automated software to log in to multiple websites with stolen username-password pairs. These credentials are typically acquired from data breaches and are tested across many platforms, exploiting users’ tendency to reuse passwords.

The attack isn’t limited to a particular type of account. It spans everything from streaming services to financial systems. The motive behind these attacks can vary from financial gain through unauthorized transactions to free access to subscription services. Credential stuffing poses a challenge for users and organizations attempting to maintain secure systems.

This is part of a series of articles about authentication.

The impact of credential stuffing attacks 

Credential stuffing attacks have widespread implications for both individuals and organizations.

For individuals, these attacks often result in unauthorized access to personal accounts, leading to potential identity theft, fraudulent transactions, and a loss of privacy. When attackers gain control over user accounts, they may sell the account information on dark web marketplaces, allowing others to exploit it further. 

For example, access to an online retail account can enable attackers to make unauthorized purchases, while access to a bank account can lead to direct financial losses.

For organizations, credential stuffing represents a significant security and financial risk. When attackers gain access to customer or employee accounts, they may access sensitive information, leading to potential data leaks, reputational damage, and regulatory penalties. The broader impact includes a loss of customer trust. 

Additionally, credential stuffing attacks place a heavy burden on IT infrastructure, as they generate a large volume of login requests in a short period. This can lead to system slowdowns or denial of service, impacting legitimate users’ access. The costs associated with investigating and mitigating these attacks, coupled with potential regulatory fines, can be expensive.

How credential stuffing works 

Credential stuffing attacks rely on stolen username-password pairs, often obtained from data breaches or purchased on the dark web. Attackers then use automated tools, like bots, to test these credentials across numerous websites, seeking accounts where users have reused the same login details. Here’s a breakdown of the typical steps involved:

1. Gathering credentials: Attackers compile lists of username-password pairs, often available on underground marketplaces or in data dumps from previous breaches. These lists can contain millions of credentials.
2. Setting up automated tools: Attackers use automated software, such as bots, to rapidly test the credentials across multiple platforms. These tools can be configured to bypass basic security measures, such as rate limiting, by using techniques like rotating IP addresses or incorporating CAPTCHA-solving services.
3. Launching the attack: The bots systematically attempt to log in to various accounts on targeted websites or services, using the credentials in rapid succession. This process enables attackers to test thousands or even millions of combinations at scale.
4. Gaining access: When a match is found, the attacker successfully gains access to an account. Depending on the target, attackers may immediately exploit the account or catalog the successful credentials for future use or resale.
5. Monetizing compromised accounts: After obtaining access, attackers may perform various actions depending on the type of account. They may make unauthorized purchases, transfer funds, steal personal data, or sell access to subscription accounts (e.g., streaming services) on the black market.

Credential stuffing vs brute force vs password spraying attacks 

While credential stuffing, brute force, and password spraying attacks all aim to gain unauthorized access to accounts, they differ in approach and technique:

1. Credential stuffing: In credential stuffing, attackers use previously obtained username-password pairs, testing them on multiple sites to exploit password reuse. Credential stuffing is efficient and stealthy because it relies on known credentials rather than randomly guessing passwords. Since attackers already have password combinations, the success rate can be relatively high, especially among users who reuse passwords across different platforms.
2. Brute force attacks: Brute force attacks involve systematically guessing passwords for a target account, often using automated tools to try every possible combination until they find the correct one. This method is computationally intensive and time-consuming, especially for accounts with strong passwords. Due to the volume of attempts required, brute force attacks are more likely to trigger security measures like account lockouts or rate-limiting.
3. Password spraying: Password spraying is similar to brute force attacks but takes a different approach to evade detection. Instead of targeting one account with many password guesses, attackers attempt a few commonly used passwords (like “password123” or “welcome1”) across a large number of accounts. This method helps avoid account lockouts, as each account only experiences a small number of login attempts. Password spraying relies on the assumption that many users choose weak, common passwords.

Defending against credential stuffing 

Here are some of the main measures that organizations can take to mitigate the risk of credential stuffing.

1. Implementing multi-factor authentication (MFA)

MFA adds an additional security layer beyond passwords by requiring secondary verification steps, like a one-time code sent to a mobile device. This complicates credential stuffing because, even with valid credentials, attackers often cannot bypass the secondary check.

2. Using CAPTCHA and bot detection

CAPTCHAs are designed to differentiate between human users and automated bots, adding friction to large-scale credential stuffing attacks. However, attackers continuously improve AI-based CAPTCHA solvers, making traditional CAPTCHAs less effective over time.

To enhance security, organizations should pair CAPTCHA with advanced bot detection techniques, such as IP reputation analysis, device fingerprinting, and behavioral analytics. Modern bot detection systems can analyze user interactions—such as mouse movements, typing speed, and navigation patterns—to distinguish legitimate users from automated threats. 

Adaptive CAPTCHAs, which only trigger under suspicious conditions (e.g., abnormal login locations or rapid login attempts), can further improve security without degrading the user experience. By combining CAPTCHA with AI-driven threat detection and anomaly monitoring, organizations can proactively block credential stuffing attempts while ensuring seamless access for legitimate users.

3. Ensuring monitoring and anomaly detection

Continuous monitoring and anomaly detection systems help identify unusual login patterns indicative of credential stuffing attacks. These systems can automatically block or flag activities deviating from normal user behavior, such as an unusual location or rapid sequence of login attempts, for further investigation.

Implementing monitoring frameworks allows organizations to respond swiftly to potential threats, minimizing damage. These solutions require fine-tuning to balance detection accuracy and false positives, ensuring legitimate users aren’t impacted while preventing unauthorized access. Regular updates to these systems help keep pace with evolving attack techniques and patterns.

4. Rate limiting and throttling login attempts

Rate limiting helps mitigate credential stuffing attacks. By capping the number of allowed login attempts over a defined timeframe, systems can help prevent automated tools from brute-forcing credentials at scale. This approach slows down attackers and reduces the likelihood of success without impeding regular user access.

Intelligent throttling systems can dynamically adjust limits based on user behavior and risk profiles, improving security. Deploying this strategy helps guard against excessive login attempts, protecting accounts, and system resources. 

5. Educating users on password hygiene

Users should be encouraged to create strong, unique passwords for each account and change them regularly. Password management tools can assist users in maintaining a vault of secure credentials without the burden of memorization.

Effective education programs highlight the importance of unique passwords and the risks of reuse, aligning user behavior with best practices. Regular communication and updates about cybersecurity threats keep users informed and mindful of evolving digital dangers. 

6. Using passwordless authentication 

Passwordless authentication removes the dependence on passwords altogether, eliminating a significant vulnerability exploited by credential stuffing. Methods include biometric verification, such as fingerprints or facial recognition, and one-time codes sent via email or mobile devices. These alternatives provide secure and user-friendly options that bypass password-based weaknesses.

However, adopting passwordless systems can present challenges, primarily in user adoption and infrastructure readiness. Ensuring a smooth transition requires clear communication and education for users, highlighting benefits and addressing concerns. 

7. Leveraging behavioral biometrics

Behavioral biometrics authenticate users based on unique patterns like typing speed, mouse movements, or interaction style, providing an additional security layer. These metrics are difficult for attackers to replicate and increase the accuracy of user authentication processes.

Implementing behavioral biometrics requires leveraging advanced analytics to create personalized profiles for users. Continuous monitoring aligns security efforts with user behavior, allowing for real-time response to anomalous activities. Although still emerging, this approach is a promising tool to combat credential stuffing.

Related content: Read our guide to authentication types

Preventing credential attacks with Frontegg

Credential stuffing attacks are evolving, and traditional defenses alone are no longer enough. Organizations need a modern, adaptive approach to identity security—one that protects user accounts without adding unnecessary friction for legitimate users.

Frontegg provides a comprehensive CIAM solution that helps businesses automate security measures, enforce adaptive authentication, and empower non-developer teams to manage identity policies without relying on engineering. With built-in MFA, bot detection, anomaly monitoring, and passwordless authentication, Frontegg ensures that your users stay secure, without compromising experience.

Ready to protect your users and reduce developer toil? Contact our sales team today to see how Frontegg can simplify and strengthen your identity security.