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Introduction:
Authentication and access control vulnerabilities remain a primary target for bug bounty hunters, offering direct pathways to critical system compromises. This guide provides a technical deep dive into the commands and methodologies used by professional security engineers to systematically uncover and exploit these flaws, turning theoretical knowledge into rewarded bounties.
Learning Objectives:
- Master command-line tools for enumerating authentication endpoints and misconfigurations.
- Develop a methodology for testing privilege escalation and horizontal/vertical access control flaws.
- Learn to validate and demonstrate the impact of identified vulnerabilities for successful bug bounty submissions.
You Should Know:
1. Web Directory and Endpoint Discovery with ffuf
`ffuf -w /path/to/wordlist -u https://target.com/FUZZ -mc 200,301,302,403 -t 100`
Ffuf is a fast web fuzzer used to discover hidden directories, API endpoints, and administrative panels. The `-w` flag specifies the wordlist path, `-u` defines the target URL with `FUZZ` marking the insertion point, `-mc` filters for successful HTTP status codes, and `-t` sets the number of concurrent threads. Hunters use this to find unprotected /admin, /api, `/config` directories that may lack proper authentication.
2. Subdomain Enumeration for Attack Surface Expansion
`subfinder -d target.com -o subdomains.txt && httpx -l subdomains.txt -o live_subdomains.txt`
Subfinder discovers subdomains through passive sources, expanding the target’s attack surface. Httpx then probes these subdomains to identify live web services. This pipeline is crucial for finding overlooked development, staging, or API subdomains that often have weaker authentication mechanisms compared to the primary domain.
- Testing for IDOR (Insecure Direct Object Reference) Vulnerabilities
`curl -H “Authorization: Bearer” http://api.target.com/v1/user/12345/profile`
Manipulate object identifiers in API requests while maintaining a valid session token. Change `12345` to another user’s ID. A successful 200 response returning another user’s data indicates a critical IDOR flaw. Always use a token from an account you control during testing and ensure you have permission to test the target.
4. JWT Token Tampering with johntheripper
`john –wordlist=rockyou.txt jwt.txt`
John the Ripper can crack weak JWT secrets. Save a JWT token to `jwt.txt` in the format token::secret. If the secret is cracked, you can forge arbitrary tokens with `jwt.io` to impersonate users, including administrators. This tests for the use of predictable or weak signing keys.
5. Testing for HTTP Verb Tampering
`curl -X POST http://target.com/admin/deleteUser -d “userid=attacked”`
`curl -X GET http://target.com/admin/deleteUser?userid=attacked`
Many applications enforce authentication on common verbs like POST but overlook others. Test alternative HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD) on sensitive endpoints. A successful action with an unexpected verb indicates a misconfigured access control rule.
6. Cookie Attribute Security Testing
`curl -I https://target.com/ | grep -i set-cookieAnalyze the `Set-Cookie` headers for missing security attributes. Look forHttpOnly,Secure,SameSite`, and `Path` attributes. Missing `HttpOnly` allows XSS token theft; missing `Secure` allows transmission over HTTP. This doesn’t directly bypass auth but identifies weak implementations that make attacks easier.
7. Testing for Authentication Bypass via URL Manipulation
`curl “http://target.com/admin../api/config”`
Path traversal sequences (../, ..\, ;, //) in URLs can sometimes bypass path-based access rules. Test by adding these sequences before or after restricted directory names. This is especially effective on misconfigured reverse proxies or application servers.
- Automated Testing with Nuclei for Known Auth Flaws
`nuclei -u https://target.com -t ~/nuclei-templates/technologies/`
`nuclei -u https://target.com -t ~/nuclei-templates/exposures/`
Nuclei templates can automatically test for thousands of known vulnerabilities, including specific authentication bypass CVEs, exposed configuration files, and default credentials. Run technology detection first to identify the stack, then run relevant exposure templates.
9. Testing for Response Manipulation (403 Bypass)
`curl -X POST http://target.com/privileged-action -H “X-Original-URL: /admin” -H “X-Rewrite-URL: /admin”`
Many applications use headers like `X-Original-URL` or `X-Rewrite-URL` for internal routing. Forward these headers with altered values to potentially bypass perimeter security controls that block direct access to /admin.
10. Session Token Analysis and Predictability
`for i in {1..100}; do curl -s -c cookie.txt https://target.com/login && cat cookie.txt | grep session; done`
Generate multiple session tokens by authenticating repeatedly. Analyze the captured tokens for patterns, predictability, or sequential generation. Weak session management allows attackers to guess or brute-force active sessions.
11. Testing for OAuth Misconfigurations
`https://target.com/oauth/authorize?response_type=token&client_id=CLIENT_ID&redirect_uri=https://attacker.com&scope=openid%20profile`
Test for OAuth flaws by manipulating the `redirect_uri` parameter to an attacker-controlled domain. If the application allows open redirects and includes an access token in the fragment, it could lead to account takeover.
12. Testing for SQL Injection on Authentication Forms
`curl -X POST https://target.com/login -d “username=admin’–&password=any”`
Basic SQL injection probes on login forms can sometimes bypass authentication entirely. The payload `admin’–` comments out the password check in vulnerable SQL queries, potentially granting access as the administrator.
13. Testing for Default Credentials on Identified Services
`hydra -C /usr/share/seclists/Default-Credentials/default-passwords.txt target.com http-form-post “/login:username=^USER^&password=^PASS^:Invalid credentials”`
Use Hydra to test common default credentials against identified login portals. Combine this with technology fingerprinting (e.g., identifying WordPress, Jenkins, Apache Tomcat) to use vendor-specific default credential lists.
14. Analyzing CORS Misconfigurations for Credential Theft
curl -H "Origin: https://evil.com" -H "Access-Control-Request-Method: GET" -X OPTIONS -v https://api.target.com/user/profile`
Test for misconfigured Cross-Origin Resource Sharing (CORS) that allows arbitrary origins. If the `Access-Control-Allow-Origin` header reflects `https://evil.com`, the API may allow authenticated requests from malicious sites, leading to data exfiltration.
15. Testing for File Upload Bypasses to Gain Execution
`curl -X POST -F "[email protected]" -F "name=shell.jpg" https://target.com/upload`
Attempt to bypass file upload restrictions by changing the `Content-Type` header toimage/jpeg, using double extensions (shell.php.jpg), or adding null bytes (shell.php%00.jpg`). A successful upload of executable content can lead to web shell installation and system compromise.
What Undercode Say:
- The automation of initial reconnaissance and vulnerability probing is no longer optional; it’s fundamental to competing in the modern bug bounty landscape.
- The most critical flaws often exist at the intersection of multiple systems (e.g., between the main application, API, and authentication server), requiring a holistic testing approach.
- Analysis: The shared post demonstrates a critical reality: foundational web vulnerabilities like broken access control remain highly prevalent and valuable. While advanced exploits attract attention, consistent methodology and mastery of core testing tools yield repeated success. The future of bug hunting lies in layered approaches—combining automated scanning for breadth with manual, reasoning-based testing for depth. As applications grow more complex with microservices and API-driven architectures, the attack surface for authentication flaws expands exponentially, ensuring these skills remain in high demand.
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Fazriansyahmuh Bugbounty – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
