Overview
Credential stuffing and stealer logs are two distinct but related threats. Understanding the difference is critical for choosing the right defensive strategy.
What Is Credential Stuffing?
Credential stuffing is an automated attack where attackers take username/password pairs leaked from one service and systematically try them against other services. The attack exploits a simple fact: people reuse passwords.
How it works:
- Attacker obtains a list of email/password pairs from a known breach (e.g., a leaked e-commerce database)
- Automated tools test those credentials against other services (email, banking, VPN, SaaS)
- Because many people use the same password everywhere, a percentage of the attempts succeed
What Are Stealer Logs?
Stealer logs come from info-stealer malware installed on a victim's device. The malware harvests all saved credentials from browsers, applications, and sometimes even session cookies.
How it works:
- A user's device is infected with info-stealer malware (via phishing, fake software, etc.)
- The malware extracts every saved password from all browsers
- The harvested data is packaged and sold on dark web marketplaces
Key Differences
| Factor | Credential Stuffing | Stealer Logs |
|---|---|---|
| Data source | Old breach databases | Active malware on devices |
| Freshness | Often months/years old | Hours to days old |
| Scope per victim | One service's credentials | ALL saved credentials across ALL services |
| MFA impact | Blocked by MFA | Session cookies can bypass MFA |
| Reuse dependency | Only works if passwords are reused | Works regardless — captures actual passwords |
| Volume | Millions of attempts, low success rate | Smaller volume, higher value per entry |
| Detection | Login anomaly detection | Credential monitoring services |
Why Stealer Logs Are More Dangerous
While credential stuffing is a well-known threat, stealer logs represent a more severe risk:
Freshness: Stealer log credentials are typically hours or days old — not years old like many breach databases. This means the passwords are more likely to still be valid.
Complete capture: Instead of one leaked credential from one service, a stealer log contains every password the victim has saved — potentially dozens of corporate credential pairs.
MFA bypass potential: Some stealers capture active browser session cookies, which can be replayed to bypass MFA entirely. The attacker doesn't need the password or the second factor.
No reuse required: Credential stuffing only works when someone reuses a password. Stealer logs capture the actual passwords for each service — no reuse needed.
Why Both Require Monitoring
Your organization needs protection against both threats:
- Credential stuffing defense: Enforce MFA, implement rate limiting on login pages, monitor for anomalous login attempts
- Stealer log defense: Deploy credential monitoring (like Verusight), implement endpoint detection, educate employees about malware risks
Verusight monitors for both — we scan breach databases (credential stuffing source material) and stealer log collections (direct malware harvest) to give you comprehensive visibility.