Anatomy of a Credential Stuffing Attack

What is credential stuffing?

Credential stuffing is a type of cyberattack where attackers use automated tools to try large volumes of username and password combinations — often obtained from a previous data breach — to gain unauthorized access to user accounts. While not the most sophisticated type of attack, credential stuffing poses a significant threat because it relies on weak passwords and password reuse. By testing millions of username-password combinations in a short span of time, attackers can compromise credentials with minimal effort. Even though the success rate is typically low, the sheer volume of user credentials available for trade on the dark web makes this tactic worthwhile. It’s often used in combination with phishing attacks to take over accounts and wreak havoc.

Why attackers use credential stuffing

Ransomware groups such as Akira, Medusa, and Blacksuit use credential stuffing as an easy way to gain access and move laterally across the corporate network. They take credentials obtained from one data breach and use the same usernames and passwords to log into a VPN or business app. The attacker is counting on employees to reuse the same credentials for multiple services, and uses bots to get around multi-factor authentication (MFA) and other prevention tools.

How does a credential stuffing attack work

Credential stuffing attacks are relatively straightforward. They typically start when the attacker uses bots or scripts to automate the process of attempting to log in using stolen credentials. These tools can try thousands of login attempts per second, allowing threat actors to efficiently test credentials across multiple platforms.

Once a login is successful, the attacker can take over the compromised account to progress through the corporate network. They can steal sensitive data, disrupt operations, and launch further attacks — without ever needing to run an exploit.

How to counter credential stuffing attacks

In the case of credential stuffing, security awareness training and other preventative security measures won’t do much — you need a way to catch stuffing attempts as they happen. But often, the only suspicious activity is a sudden increase in login attempts. And even then, it’s difficult to stop attacks without impacting legitimate users.

The best way to stop credential stuffing attacks is with 24/7 monitoring supported by AI-driven detections, such as those provided by Vectra AI. For example, when a real-world attacker attempted to log in to a global organization’s Microsoft SaaS environment, it triggered multiple Vectra AI detections including Entra ID suspicious sign-on and unusual scripting engine usage. These detections prompted Vectra’s MXDR team to escalate the incident and stop the attack before it started. 

See how Vectra MXDR stopped a credential stuffing attack

Check out our attack anatomy below to see what happened when a real-world attacker attempted to infiltrate a Vectra AI customer’s environment using credential stuffing.