What is Credential Stuffing?

Credential stuffing is a type of cyberattack where attackers use automated tools to attempt to gain unauthorized access to multiple online accounts by exploiting previously stolen or leaked usernames and passwords. Attackers rely on the fact that many users reuse the same login credentials across different websites and services. By taking advantage of this common behavior, they can successfully access accounts without needing to crack passwords individually.

Why Credential Stuffing is a Concern

Credential stuffing poses a significant threat to both individuals and organizations. For individuals, it can lead to unauthorized access to sensitive information, financial loss, and identity theft. For organizations, these attacks can result in data breaches, financial penalties, and damage to their reputation.

How Hackers Use Credential Stuffing

Hackers use credential stuffing as a methodical and efficient way to exploit the widespread habit of password reuse across multiple online accounts. Here’s how the process typically unfolds:

1. Acquisition of Credentials: Hackers begin byobtaining large databases of usernames and passwords. These credentials areoften harvested from previous data breaches, where user information wasexposed. These databases can be found for sale on the dark web or exchangedamong cybercriminals.

2. Automated Tools: Once the credentials are in hand,hackers employ automated scripts or bots specifically designed for credentialstuffing. These tools are capable of quickly testing thousands or even millionsof username-password combinations across multiple websites and services.

3. Target Selection: Hackers usually target popularwebsites where users are likely to have accounts, such as banking sites,e-commerce platforms, social media networks, and email providers. The idea isthat if they can gain access to one of these accounts, they can leverage it forfinancial gain, identity theft, or further attacks.

4. Account Takeover: When the automated tools find asuccessful match—where a username and password pair work on a targeted site—thehacker gains unauthorized access to the account. This is known as an accounttakeover. The hacker can then change the password, lock out the legitimateuser, steal sensitive information, make unauthorized transactions, or use theaccount for further attacks, such as phishing or spreading malware. 

5. Scaling the Attack: Credential stuffing can behighly scalable. Hackers may simultaneously target multiple websites, rapidlytesting credentials across different platforms. The more successful logins theyachieve, the greater the potential payoff.

6. Lateral Movement: Once inside an account, hackersoften look for additional opportunities. For example, they might check if thecompromised account is linked to other services (like email accounts, cloudstorage, or payment platforms) and use it to access these as well. This lateralmovement increases the attack's impact and can lead to further breaches ofsensitive data.

7. Monetization: Finally, the stolen accounts areeither exploited directly—through fraudulent purchases, draining bank accounts,or stealing personal data—or sold on the dark web to other cybercriminals.These accounts are valuable commodities, especially those tied to financialservices, social media, or corporate environments.

How to Prevent Credential Stuffing

To defend against credential stuffing, it's crucial to implement security measures such as:

Use Multi-Factor Authentication (MFA)

Require an additional verification step beyond just the username and password, such as a security key or biometric validation. Learn more about MFA and The Challenges of MFA Everywhere.‍

Use Unique Passwords and Automate Password Rotation

Encourage users to create strong, unique passwords for each of their accounts. Additionally, automating password rotation after an account is breached can help contain the risk and prevent unauthorized access from spreading to other accounts. Learn more about Grip's automated password rotation.

Implement SSO

Implementing Single Sign-On (SSO) can significantly reduce the risk of credential stuffing by centralizing authentication and minimizing the need for users to remember multiple passwords. With SSO, users authenticate once and gain access to various applications, reducing the chances of password reuse across different sites, which is a common vulnerability exploited in credential stuffing attacks.

Conclusion

Credential stuffing is particularly dangerous because it doesn’t require sophisticated hacking skills—just access to breached credentials and the right tools. This makes it a favored method among cybercriminals, contributing to its widespread use and the growing number of associated breaches. Organizations must stay vigilant and adopt robust SaaS identity security practices to protect themselves and their users from this increasingly common form of attack.