Credential Stuffing Prevention & Testing
Your customers reuse passwords. Attackers know this. We simulate large-scale credential stuffing attacks (OWASP OAT-008) against your online banking, payment platforms, and investment accounts to validate that your rate limiting, bot detection, and MFA controls stop automated account takeover before it reaches production.
Credential Stuffing Testing:
Beyond Rate Limiting
Rate limiting alone fails against distributed botnets. Our consultants follow OWASP OAT-008 methodology to simulate the full credential stuffing attack chain: breach database harvesting, simulated residential proxy rotation, CAPTCHA defeat, and MFA fatigue attacks.
Credential Stuffing Simulation
Ethical simulation of automated OWASP OAT-008 attacks using breach databases and botnet techniques. We test against large-scale automated login attempts using stolen username/password pairs from major data breaches, validating detection, rate limiting, and lockout mechanisms against realistic attack scenarios targeting online banking and payment portals.
Rate Limiting & CAPTCHA Bypass
Advanced testing of anti-automation controls including rate limiting, CAPTCHA challenges, and progressive delays. We simulate attackers using distributed botnets, simulated residential proxy networks, and CAPTCHA-solving services to bypass traditional defenses.
Bot Detection Evasion
Testing device fingerprinting, behavioral analytics, and bot detection systems using advanced evasion: simulated residential proxy rotation, user-agent randomization, JavaScript execution environments, mouse movement simulation, and realistic timing patterns.
MFA Implementation Testing
Assessment of MFA implementation weaknesses including bypass through backup authentication methods, push notification fatigue, and session management flaws allowing credential stuffing despite MFA deployment.
Breach Database Exposure
Analysis of dark web sources to identify your customers' exposed credentials. We assess organizational credential exposure, validate breach notification procedures, and test proactive password reset capabilities.
Post-Auth Session Abuse
Once credentials are validated, attackers exploit weak session management to maintain persistence. We test session fixation, token replay, concurrent session limits, and session hijacking to validate that compromised credentials cannot be weaponised at scale.
Credential Stuffing Risk Profile
Password reuse makes credential stuffing the most cost-effective attack vector against financial services. 12+ billion breached credentials are available to attackers for under £50.
Breached Credentials
Attackers purchase targeted credential lists for £5-50 and automate testing across thousands of financial platforms.
Attack Success Rate
Even 0.1% means 10,000 compromised accounts from 10 million attempts. Each banking account yields £2,500-25,000 in fraud.
Compliance Frameworks
Testing satisfies PSD2 SCA, GDPR Art. 32, FCA PS21/3, and OWASP OAT-008, documented for auditors.
Controls
What We Find That Scanners Cannot.
Anonymised examples from recent credential stuffing assessments. These are the critical authentication weaknesses that automated tools are incapable of detecting.
Rate Limiting Bypass via Simulated Residential Proxies
Per-IP rate limiting was the sole anti-automation control. Testing demonstrated that rotating through 5,000 simulated residential proxy IPs allowed sustained credential stuffing at 50,000 attempts per hour without triggering any alert or lockout.
MFA Fatigue Attack on Push Notifications
After validating stolen credentials, repeated authentication push notifications were sent to the victim. No limit on push frequency and no user feedback mechanism existed, allowing fatigue-based MFA bypass within 15 minutes of sustained requests.
CAPTCHA Bypass via Solving Service Integration
reCAPTCHA v2 was deployed on the login endpoint but the server accepted tokens up to 120 seconds old. Integration with a commercial CAPTCHA-solving service achieved 94% solve rate at £2.99 per 1,000 solves, rendering the control ineffective at scale.
Credential Exposure in Error Response
Login failure responses returned different error messages for invalid usernames versus invalid passwords. This enumeration vulnerability allowed attackers to first validate which breached email addresses had active accounts, then target only confirmed accounts with credential stuffing.
When Do Organisations Commission This Test?
Credential stuffing testing is typically triggered by one of these six scenarios. If any apply, you are in the right place.
Account Takeover Incidents
Customers are reporting unauthorised access to their accounts. Fraud losses are increasing and your current controls are not stopping credential stuffing at scale.
PSD2 SCA Audit
Your auditor has flagged PSD2 Strong Customer Authentication as a control gap and requires independent evidence that your authentication defenses resist automated attacks.
New Digital Banking Platform
A new customer-facing portal or mobile banking app is approaching launch and you need to validate authentication security before go-live.
Breach Database Exposure
A third-party breach has exposed your customers' credentials. You need to assess your exposure and validate that proactive password reset workflows and breach notification procedures are working.
Bot Traffic Anomalies
Your WAF or analytics show suspicious authentication traffic patterns (high login failure rates, geographic anomalies, non-human timing) but you cannot confirm whether your defenses are holding.
Cyber Insurance Renewal
Your insurer requires evidence of authentication security testing, including credential stuffing resilience, as a condition of policy renewal or favourable premium.
Mapped directly to your regulatory controls.
Our CREST-certified report includes a compliance mapping matrix that cross-references our technical findings to the specific framework clauses your auditor requires.
PSD2
Strong Customer Authentication for electronic payments
GDPR
Appropriate technical measures for data protection
FCA PS21/3
Operational resilience testing for important business services
OWASP OAT
Credential stuffing and CAPTCHA defeat classification
NIST 800-63B
Digital identity authentication assurance levels
PCI DSS v4.0
Strong authentication for cardholder data environment access
Globally Accredited Consultants
All testing is conducted by CREST-certified professionals.
Engagement Workflow
Structured to minimise operational friction and maximise the value of the testing window.
Breach Exposure Assessment
Comprehensive analysis of your customer credential exposure across public breach databases and dark web sources. We establish baseline risk and identify the scale of credential reuse affecting your platform.
Credential Stuffing Simulation
Ethical credential stuffing attacks using client-authorized test accounts with distributed proxy rotation, realistic timing patterns, and botnet behavior simulation.
Detection Gap Analysis
We document which controls held and which failed: rate limiting bypass methods, CAPTCHA defeat techniques, bot detection evasion, and MFA bypass opportunities.
Report & Debrief
Encrypted delivery of your Executive and Technical reports, followed by a debrief call to walk through findings, prioritised remediation guidance, and next steps.
What You Get
Every credential stuffing assessment includes the following deliverables, formatted for both technical teams and non-technical stakeholders.
Reports are delivered via our real-time penetration testing portal with role-based access. Also available in PDF and DOCX formats.
Close the Loop.
After the Test.
Your credential stuffing assessment identifies what is exploitable today. We feed those exact findings into our 24/7 Managed SOC, building custom detection rules for credential stuffing attempts, account takeover patterns, and breach database exposure alerts.
Explore Defensive ServicesReal-Time ATO Detection
Custom detection rules for credential stuffing patterns and account takeover attempts.
Breach Database Monitoring
Continuous monitoring of dark web sources for customer credential exposure.
Incident Response
Immediate containment and forensic investigation for confirmed account takeover incidents.
Web App Pen Testing
Full OWASP web application penetration testing beyond authentication endpoints.
Full Penetration Testing Catalogue
Comprehensive penetration testing services tailored to your environment.
Internal Testing
Post-perimeter assessments targeting Active Directory, lateral movement, privilege escalation, and segmentation validation from inside your network.
The best time to test your defences is now.
Join the high-growth companies relying on Precursor for continuous offensive and defensive security.
Frequently Asked Questions
Common questions about this service, methodologies, and deliverables.
Credential stuffing prevention testing typically costs between £5,000 and £12,000+ depending on application complexity, number of authentication endpoints, and testing scope. Standard testing for online banking or payment portals averages £6,500 for comprehensive attack simulation including botnet behavior, proxy rotation, breach database analysis, and bot detection evasion testing. Extensive testing for multi-application financial platforms with complex authentication flows (mobile apps, web portals, API gateways) typically costs £8,000-£12,000. We provide fixed-price quotes after reviewing your authentication architecture and customer volume.
Credential stuffing (OWASP OAT-008) is an automated attack using stolen username/password pairs from data breaches. Attackers use breach databases containing billions of credentials to attempt logins across multiple services, exploiting password reuse. Password spraying tries common passwords against many usernames. Credential stuffing has higher success rates (0.1%-2%) because credentials are valid somewhere. They are simply being tested on your platform.
Yes, for several reasons: (1) MFA coverage gaps: many organizations only enforce MFA for high-value transactions, not all logins, allowing attackers to perform reconnaissance and prepare fraud before MFA triggers. (2) MFA bypass vulnerabilities: testing validates that MFA cannot be bypassed through backup authentication methods, session hijacking, or registration flow abuse. (3) Regulatory validation: PSD2 requires testing Strong Customer Authentication (SCA) effectiveness, not just implementation.
Professional credential stuffing testing is designed to be safe and non-disruptive. We use dedicated test accounts (not real customer credentials), rate-limited attack simulation (realistic but controlled volumes), coordinated testing windows during low-traffic periods, and immediate abort procedures if any service degradation is detected. We can also test in staging/pre-production environments that mirror production authentication flows.
Credential stuffing testing is a specialized form of penetration testing focusing exclusively on automated account takeover attacks. Standard penetration testing covers broad vulnerabilities (SQL injection, XSS, business logic flaws) but typically does not include large-scale automated attack simulation with breach databases, distributed botnet behavior, simulated residential proxy rotation, and advanced bot detection evasion. Think of it as offensive security for authentication systems specifically.
Success rates vary by industry and implementation: 0.1%-2% for well-protected financial services with MFA and bot detection, 2%-5% for e-commerce and entertainment platforms with weaker controls, and up to 10%+ for sites without rate limiting or bot protection. Even 0.1% success means 10,000 compromised accounts from 10 million login attempts. Financial services are high-value targets. A single compromised banking account can yield thousands in fraudulent transfers before detection.
Simple rate limiting (per-IP) is easily bypassed using distributed botnets and simulated residential proxy networks. Attackers rotate through thousands of IP addresses (or 10,000+ in sophisticated botnets), staying below per-IP rate limits while testing millions of credentials. Effective defenses require distributed rate limiting (tracking attempts across IP, account, session), device fingerprinting, behavioral analytics, and breach database integration.
Financial impacts include direct fraud losses (average £2,500-25,000 per compromised account in banking), regulatory fines under PSD2 for failing to prevent unauthorized transactions, ICO penalties for data breach notification failures, and reputational damage. PSD2 Strong Customer Authentication (SCA) requires two-factor authentication for electronic payments. Account takeover also violates GDPR Article 32 (security of processing) with potential fines up to €20M or 4% global turnover.
Layered defense is essential: (1) Multi-Factor Authentication (MFA), mandatory for financial transactions. (2) Device fingerprinting identifies attack tools despite IP rotation. (3) Behavioral analytics detects non-human login patterns. (4) Breach database integration blocks known compromised passwords proactively using HIBP API. (5) Distributed rate limiting tracks attempts across IP, account, and session. (6) Web Application Firewall (WAF) with bot protection identifies automated tools.