What is a credential stuffing attack—and how can you help prevent it?

Billions of stolen usernames and passwords are circulating on the dark web. According to the Verizon 2025 Data Breach Investigations Report, 88% of hacking breaches in 2024 were caused by stolen or brute-forced credentials. But the stolen credentials, used in credential stuffing attacks, are often far more dangerous.

So what is credential stuffing, and how could it affect you? Most importantly, how can you help prevent it? 

What is credential stuffing?

Credential stuffing attacks cram different combinations of usernames and passwords found in credential dumps into login pages until an account is unlocked. They are an increasingly common cyber attack—mostly because users often reuse their usernames and passwords. If a user's login information is stolen from one place, it will likely work elsewhere.

Credential stuffing attacks vs. brute force attacks

So, what’s the difference between a credential stuffing attack and a brute force attack? Credential stuffing attacks are considered more effective than brute-force attacks because they are not a total guessing game—they leverage existing username and password information. They are also harder to detect, and they are not easily thwarted by routine security protections, such as a cap on failed attempts from a single computer.

Unlike credential stuffing attacks, brute force attacks involve guessing login information and passwords. A simple brute force attack often uses automated tools to do this. Weak passwords can often be cracked in seconds, while strong passwords take a bit longer.

How does a credential stuffing attack work?

There are so many stolen credentials circulating online nowadays that their price is down nearly to zero. Attackers can acquire these lists for cheap and feed the information to bots and have them crack open accounts on target sites. Success rates are low—Shape Security estimates success rates between 0.2% to 2%—but the costs are so modest that the rewards can still provide a significant return on the investment.

Like many cyber security problems, credential stuffing is a constant cat-and-mouse game. When website operators limited the number of login attempts from one IP address, attackers responded by feeding bots spoofed addresses. Secondary authentication methods like CAPTCHA codes were effective, but only for a short time.

How does a credential stuffing attack work?

While nothing is foolproof, the easiest way to avoid becoming a victim of credential stuffing is to stop reusing passwords. Password managers are abundant and user-friendly, but despite their ubiquity, not everyone uses them, —and many who do probably don't use the feature that autogenerates secure passwords.

Website operators can protect themselves by employing multi-factor authentication, which uses a secondary form of identity verification, such as a unique code texted to a cellphone. Multi-factor authentication can help prevent 99.9% of account compromise attacks, Microsoft says, but adoption has been slow.

Threatpost reported that more than three-quarters of Microsoft 365 administrators don't enable the built-in multi-factor authentication option—an alarming figure considering that many of those accounts are behind corporate firewalls.

Consumers can leverage tools such as Have I Been Pwned? to learn whether their accounts have been compromised. Website operators should advise their customers against reusing passwords and persuade them to deploy multi-factor authentication and single-use login credentials.

Now that you have an answer to the question, “what is credential stuffing,”evaluate your security program with Verizon's Security Program Assessment.

The author of this content is a paid contributor for Verizon.