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What is Credential Stuffing?
Credential stuffing is when attackers take usernames and passwords leaked from one breach and automatically try them on other services. Because most people reuse passwords, a breach at a shopping site or social network can give attackers working credentials for your corporate email, VPN, or cloud platforms. It is automated, fast, and alarmingly effective.
How a Credential Stuffing Attack Works
Acquire leaked credential databases
Attackers purchase or download massive databases of usernames and passwords from previous data breaches — billions of credentials are available on dark web marketplaces.
Filter for target organization emails
They search the database for email addresses matching your company's domain, instantly identifying which employees have had credentials exposed in past breaches.
Automate login attempts
Using specialized tools, they try each leaked username-password combination against your email, VPN, cloud apps, and other services — testing thousands of combinations per minute.
Exploit successful logins
When a password still works (and it does more often than you'd expect), the attacker gains legitimate access that's nearly impossible to distinguish from a real employee logging in.
Real-World Example
A financial services firm discovered that 340 of their employees' corporate email addresses appeared in breach databases from compromised third-party services. Seventeen of those credentials still worked for the company's VPN because the employees had reused passwords. Attackers had been quietly accessing internal systems for three months before detection.
How AiVERSARY Detects Credential Stuffing Risk
AiVersary's OSINT reports check dark web breach databases and paste sites to identify which of your employees' corporate credentials have been exposed. The report shows exactly which accounts are at risk, when the breach occurred, and whether the exposed passwords suggest patterns that put other accounts in danger.
Is your organization exposed to credential stuffing?
AiVERSARY scans your public footprint and identifies the exact data attackers would use against you. $499 per report.
Get Your Threat ReportRelated Terms
MFA Fatigue
MFA fatigue is an attack where a criminal who already has your password repeatedly triggers multi-factor authentication prompts — the push notifications on your phone — until you approve one just to make them stop. It exploits the very security measure designed to protect you by turning it into an annoyance that people instinctively dismiss. This technique has been used in several high-profile breaches.
Tenant Compromise
Tenant compromise is when an attacker gains administrative control over your organization's cloud environment — your Microsoft 365 tenant, Google Workspace, or AWS account. Unlike stealing a single employee's password, this gives the attacker the keys to everything: every email, every file, every application, and every user account in your cloud infrastructure. It is the most devastating outcome of a successful credential attack.
OSINT Reconnaissance
OSINT reconnaissance — Open Source Intelligence gathering — is the first phase of nearly every targeted cyberattack. It's the process of collecting publicly available information about an organization and its people to plan an attack. Everything from your company website and LinkedIn profiles to job postings, DNS records, and conference presentations becomes intelligence. This is exactly the same process AiVersary uses, but we do it first so you can fix what's exposed.