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. Unauthorized access is illegal.
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 without logging in - JWT Tampering: Modifying token claims (e.g., “alg”: “none”)
- Password Reset Poisoning: Hijacking reset tokens via Host header injection
- Session Fixation: Forcing a known session ID on a victim
- OAuth Misconfiguration: Exploiting improper redirect URIs
- 2FA Bypass: Brute-forcing OTPs or response manipulation
- API Key Leakage: Finding keys in client-side JS code
- Default Credentials:
admin:adminorroot:toor
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=us**@****im.com&x-forwarded-host=attacker.com
Tools of the Trade
| Tool | Purpose | Example Use |
|---|---|---|
| Burp Suite | Intercepting/modifying requests | Changing response {"admin":false} to true |
| Hydra | Brute-force attacks | hydra -l admin -P pass.txt target.com http-post-form |
| jwt_tool | JWT manipulation | python3 jwt_tool.py token -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 (e.g., 5 failed attempts = 15 min lockout)
- Require strong passwords (12+ chars, mixed types)
- Use Multi-Factor Authentication (MFA/2FA)
- Secure session management (HttpOnly, Secure, SameSite cookies)
- Regularly audit authentication logs for anomalies
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/FIDO2) where possible to eliminate password-related vulnerabilities entirely.
Real-World Case Studies
Case 1: JWT Algorithm Switch
A major SaaS platform accepted JWTs with the “none” algorithm signature, allowing attackers to simply remove the signature section and forge admin tokens.
Case 2: Password Reset Hijacking
A popular social media site leaked password reset tokens in the Referer header when users clicked links in emails, allowing third-party analytics sites to capture the tokens.
Case 3: OAuth Redirect Manipulation
A financial service improperly validated the OAuth redirect_uri parameter, allowing attackers to steal access tokens via an open redirect vulnerability.
Conclusion
Broken authentication remains a critical vulnerability because:
- It provides direct access to sensitive systems without needing further exploits.
- Many developers underestimate the complexity of secure auth logic.
- Legacy systems often rely on outdated mechanisms like MD5 hashing.
Remember: Authentication security requires defense in depth – no single control is sufficient against determined attackers.