Credential stuffing attacks: How they work & tips for prevention

Credential stuffing attacks are on the rise, and they’re not going away any time soon. As long as users continue to reuse passwords and attackers have easy access to breach data, the threat will persist. And with recent reports suggesting the volume of compromised credentials has shot up by 160% so far in 2025, it seems hackers have more access to data than ever before.

The best way to avoid becoming the next victim of a credential stuffing attack is to understand how they work. In this blog, we’ll explain what credential stuffing is, how it usually plays out, and what your organization can do to detect and prevent it.

What is credential stuffing?

Credential stuffing is a type of cyberattack where attackers use stolen username and password combinations, usually obtained from a past data breach, to try to log in to other accounts across different platforms.

This method relies on the assumption that many people reuse the same credentials across multiple accounts – for example, they might use the same username and password for both online shopping and online banking. This means if attackers can get hold of a set of credentials from one platform, they can often gain unauthorized access to other platforms without needing to crack or guess passwords.

Unfortunately, password reuse is extremely common. A study from Bitwarden found that 72% of Gen Z respondents admitted to reusing passwords and 35% revealed that they never or rarely update their password after a data breach. That gives attackers plenty of opportunities to take advantage of exposed credentials.

Is credential stuffing a type of brute force attack?

Credential stuffing is generally classified as a subset of brute force attack, including by OWASP. However, there is an important distinction between the two attack types.

In traditional brute force attacks, hackers attempt to guess passwords by trying every possible combination (or using dictionary attacks) until they’re successful, usually with the help of bots. Credential stuffing, on the other hand, uses known, valid credentials exposed in data breaches. The “brute force” aspect comes from the automation and scale, not the password guessing.

So while both involve automated login attempts, credential stuffing is far more efficient and harder to detect if not properly mitigated.

Password spraying vs. credential stuffing

These two attacks are often confused, but they work in fundamentally different ways. Credential stuffing targets many accounts with known, good credentials, while password spraying targets many accounts with a few commonly used weak passwords (like Password1).

Both can evade traditional detection mechanisms, but credential stuffing is particularly dangerous because it makes use of real credentials that users trust.

How does a credential stuffing attack work?

A typical credential stuffing attack follows a straightforward but effective process:

1. Data acquisition: The first step involves the attacker obtaining leaked credentials from previous breaches. They will often purchase these on dark web marketplaces or find them in open-source dumps.
2. Target identification: The attacker selects target applications or services to test the credentials against. These are often high-value platforms like banking, e-commerce, or enterprise portals.
3. Automation and tooling: Attackers configure bots or automated credential stuffing tools to launch high-volume login attempts across many sites, using the stolen credential lists.
4. Credential testing: The bots attempt logins at scale, looking for successful matches.
5. Exploitation: Successful logins can lead to financial fraud, data theft, further lateral movement, or the sale of valid credentials.

This method is appealing to attackers because it requires minimal effort and can be massively scaled, especially when organizations lack basic protections like rate limiting or multi-factor authentication.

Statistics usually place the success rate of credential stuffing attacks somewhere between 0.1% and 2%. That may not seem like a lot, but on the scale at which these attacks play out, that can add up to hundreds or thousands of compromised accounts.

Real examples of credential stuffing attacks

Credential stuffing has been at the heart of many high-profile breaches in recent years. Here are a few notable cases:

• Roku (2024): Roku suffered two major credential stuffing attacks, affecting around 591,000 accounts overall. Attackers used breached credentials from other sites to access Roku accounts and commit unauthorized purchases, prompting Roku to implement two-factor authentication for all accounts.
• PayPal (2023): Payment platform PayPal reported that an estimated 35,000 accounts were breached in a credential stuffing attack in 2023, which involved attackers using credentials obtained in a previous data leak.
• Zoom (2020): Over 500,000 Zoom credentials were found for sale on the dark web in 2020. The credentials were gathered through credential stuffing, with hackers targeting Zoom after widespread remote work adoption.

In each case, the root issue was not a flaw in the target system’s password storage, but in users reusing compromised credentials across multiple accounts.

How to detect credential stuffing

Credential stuffing can be very difficult to detect; because it uses real login credentials, it mimics the behavior of a legitimate user. That said, there are patterns involved, which may look benign on the surface but reveal malicious behavior at scale.

Some common indicators to watch out for include:

• Unusual login patterns: A sudden spike in failed login attempts or logins from multiple geographic regions in a short timeframe are a classic indicator of suspicious activity.
• Increased bot activity: Detection of automated bot behavior, such as very rapid login requests, use of varied user agents, or attempts to bypass CAPTCHAs, often accompanies credential stuffing.
• High volume of account lockouts: An increase in users being locked out of their accounts due to failed login attempts can indicate automated testing of credentials.
• Unauthorized purchases or unusual account activity: This is usually a sign that credential stuffing has succeeded, and hackers have gained access to an account.

How to prevent credential stuffing attacks

Preventing credential stuffing can be tricky, but there are steps you can take to help protect your organization from it.

1. Enforce multi-factor authentication (MFA)

Implementing MFA for all accounts is one of the most effective methods for preventing credential stuffing attacks from being successful. Requiring users to verify their identity through a secondary method adds a critical barrier that can prevent attackers from gaining access to accounts, even if they have valid credentials.

2. Educate users on password hygiene

Provide regular employee training on the importance of using strong, unique passwords across accounts, and the dangers of password reuse.

3. Monitor for breached credentials

Identifying and remediating compromised credentials before they’re used in an attack is vital for preventing credential stuffing. With Specops Password Auditor, you can get a free, read-only audit of your Active Directory that checks accounts and passwords against 1 billion vulnerable credentials obtained from data breaches. Download for free today to scan for weak and compromised passwords.

4. Implement rate limiting

Set thresholds to limit the number of login attempts from a single IP address or account within a specific time period. This can slow down or stop automated credential stuffing attacks before they reach a large scale.

5. Block suspicious automation and bots

Use bot detection and mitigation tools like CAPTCHA, browser fingerprinting, or behavioral analysis to identify and block automated login attempts. These technologies help differentiate between legitimate users and malicious bots trying to exploit stolen credentials.

Prevent users from choosing compromised passwords

Credential stuffing attacks thrive on weak and compromised credentials, which means stopping them starts with strong password policies.

Specops Password Policy strengthens your defenses by enforcing custom password rules and blocking the use of compromised passwords in real time. With access to a growing database of over four billion known breached passwords, it automatically alerts users when their passwords are found in active attack lists and guides them to create secure, compliant alternatives.

Protect your organization from credential stuffing with smarter password enforcement. Try Specops Password Policy for free today.