Credential Stuffing: How Attackers Exploit Stolen Passwords

Credential stuffing is an automated attack technique that involves mass-testing stolen username-password pairs against multiple online services. The attack exploits a widespread human behavior: reusing the same password across multiple accounts. If a leaked password works on one service, there is a good chance it works on others too.

How does it work?

Attackers use lists of millions of email-password pairs, called combo lists, sourced from data breaches, infostealer logs, or aggregated leaks from multiple origins. These lists are then fed into automated tools (bots) capable of testing thousands of login attempts per minute against target websites.

Credential stuffing tools use sophisticated techniques to bypass protections: rotating residential proxies to mask the origin of requests, simulating human behavior to fool CAPTCHAs, and distributing attempts over time to avoid detection by rate-limiting systems.

When a username-password pair works, the attacker gains control of the account. They can then exfiltrate personal data, perform fraudulent transactions, resell the access to other criminals, or use the account as a springboard for more targeted attacks within the organization.

Why does it matter?

According to an Akamai report, over 193 billion credential stuffing attempts were recorded in a single year. This technique is one of the most cost-effective attacks for cybercriminals because it requires minimal investment: combo lists cost a few dollars and automation tools are freely available on underground forums.

For businesses, the consequences are severe: compromised customer accounts, unauthorized access to internal systems, direct financial losses, and reputational damage. The most targeted sectors include e-commerce, financial services, SaaS platforms, and streaming services.

The primary risk factor is password reuse. Studies show that over 60% of users reuse the same password across at least two different services. Every new credential leak therefore directly fuels future credential stuffing attacks.

How Stealed protects you

Stealed detects your employees’ credentials in combo lists and infostealer logs before they are exploited in credential stuffing attacks. By monitoring Telegram channels, forums, and dark web marketplaces in real time, Stealed alerts you as soon as a password associated with your domains is exposed.

This early detection allows you to force a password reset before the attack occurs, significantly reducing the window of exposure.

Learn more: read our comprehensive guide on combo lists and credential stuffing for a deeper understanding of the problem and detailed protection measures.

Start monitoring for free to detect compromised credentials before attackers exploit them.