Credential Stuffing
Last updated: January 16, 2026
Credential stuffing uses leaked username/password combinations from data breaches to attempt logins on other sites, exploiting password reuse.
Scan for This VulnerabilityWhat is Credential Stuffing?
When other sites get breached, attackers obtain millions of email/password pairs. Since many people reuse passwords, attackers automatically try these credentials on other popular sites. Even if your site was never breached, your users' accounts can be compromised.
Why It's Dangerous
This vulnerability can allow attackers to access sensitive data, compromise user accounts, or gain unauthorized control over your application. In AI-generated code, this issue is particularly common because security measures are often deprioritized in favor of rapid feature development.
Why AI Code Is Vulnerable
AI code generation tools focus on producing functional code quickly. They often generate patterns that work correctly but lack the defensive measures experienced security engineers would implement. This makes credential stuffing particularly prevalent in vibe-coded applications.
Understanding the Technical Details
Credential Stuffing is classified as a high-severity vulnerability because of its potential to cause significant damage to your application and users. Understanding the technical mechanics helps you recognize and prevent this issue in your own code.
This vulnerability typically occurs when security controls are either missing entirely, improperly configured, or incorrectly implemented. In many cases, the code appears to work correctly during development and testing, but the security flaw becomes exploitable once the application is deployed and accessible to malicious actors.
Attackers actively scan for this type of vulnerability using automated tools. Once discovered, exploitation can be rapid—often within hours of your application going live. The consequences range from data theft and account takeover to complete system compromise depending on the application's architecture.
For vibe-coded applications built with platforms like Lovable, Bolt.new, Replit, or v0.dev, this vulnerability appears in roughly 20-40% of deployments according to security research. The AI-generated patterns often follow insecure defaults that require manual security hardening.
How It Happens
- Users reusing passwords across sites
- No rate limiting on login
- No breach detection
- No multi-factor authentication
- No credential monitoring
Impact
Mass account compromise
Data theft across users
Fraud and unauthorized transactions
Reputation damage
How to Detect
- Monitor for distributed login attempts
- Check for unusual login patterns
- Track login success/failure ratios
- Use breach databases to check passwords
How to Fix
Check passwords against breach databases
Block known compromised passwords.
// Using HaveIBeenPwned API
import { pwnedPassword } from 'hibp';
const breachCount = await pwnedPassword(password);
if (breachCount > 0) {
throw new Error('This password was found in data breaches');
}Require MFA for sensitive accounts
Second factor defeats credential stuffing.
// Supabase MFA
const { data, error } = await supabase.auth.mfa.enroll({
factorType: 'totp'
});
// Require MFA verification
const { data: challenge } = await supabase.auth.mfa.challenge({
factorId: factorId
});Implement login anomaly detection
Flag suspicious login patterns.
// Check for anomalies
const isAnomaly =
newLocation ||
newDevice ||
unusualTime ||
rapidAttempts;
if (isAnomaly) {
await sendVerificationEmail(user);
await requireMFA(user);
}Commonly Affected Platforms
Prevention Best Practices
The most effective approach to credential stuffing is prevention. Implementing security measures during development is significantly easier and less costly than remediating vulnerabilities after deployment.
Security-First Development
When using AI code generation tools, always review the generated code for security implications. AI tools prioritize functionality over security, so treat all generated code as requiring security review. Establish a checklist of security requirements specific to your application type and verify each before deployment.
Continuous Security Testing
Integrate security scanning into your development workflow. Run scans after major code changes, before deployments, and on a regular schedule for production applications. Early detection of vulnerabilities reduces remediation costs and prevents potential breaches.
Defense in Depth
Never rely on a single security control. Implement multiple layers of protection so that if one control fails, others still protect your application. For example, combine authentication, authorization, input validation, and output encoding to create comprehensive protection against attacks.
Stay Informed
Security threats evolve constantly. Follow security researchers, subscribe to vulnerability databases, and monitor your dependencies for known issues. Understanding emerging threats helps you proactively protect your applications before attackers exploit new techniques.
Is Your App Vulnerable?
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Get Starter ScanFrequently Asked Questions
How is credential stuffing different from brute force?
Brute force guesses passwords randomly or from common lists. Credential stuffing uses actual leaked credentials from other breaches. It's more effective because these are real passwords people used elsewhere. Defense: breach checking, MFA, and educating users not to reuse passwords.
Should I check if passwords are in breach databases?
Yes. Services like HaveIBeenPwned provide APIs to check if a password has appeared in known breaches (using k-anonymity for privacy). Block breached passwords at signup and prompt existing users to change them. This significantly reduces credential stuffing success.