Form Fuzzer Skill

Form Fuzzer Skill

Test form inputs with edge case payloads to find security vulnerabilities and encoding issues.

When to Use

• Security testing forms for XSS/SQLi vulnerabilities
• Testing input validation and sanitization
• Finding unicode/encoding handling issues
• Checking length limit enforcement
• Pre-deployment security checks

Flags

--fuzz                           Enable fuzzing mode
--fuzz-category <category>       Category: xss | sqli | unicode | length | all (default: all)

Fuzzing Categories

Category	Purpose	Payload Count
xss	Test XSS sanitization	15 payloads
sqli	Test SQL injection prevention	12 payloads
unicode	Test encoding handling	10 payloads
length	Test length limits	4 payloads
all	All categories combined	41 payloads

Behavior

When --fuzz is active:

1. Discovery: Find all form inputs on the page
2. Classification: Identify input types (text, email, password, search, etc.)
3. Injection: For each input, try payloads from selected category
4. Observation: Check response for each payload:
   • Sanitized: Payload escaped/stripped (PASS)
   • Rejected: Clear error message (PASS)
   • Executed: XSS/SQLi worked (CRITICAL)
   • Error: Application error/crash (MAJOR)
   • Stored: Payload persists in DOM (CRITICAL)
5. Reporting: Generate security-focused report section

Response Classification

XSS Detection

// Check if script executed
// Check if payload appears unescaped in DOM
// Check for alert/console activity
// Check if event handlers fire

SQL Injection Detection

// Check for database error messages
// Check for unusual response time (time-based)
// Check for data leakage
// Check for error 500 responses

Encoding Issues

// Check for garbled text
// Check for broken layout (RTL markers)
// Check for missing characters
// Check for incorrect rendering

Length Handling

// Check if input truncated
// Check for overflow errors
// Check for client-side crashes
// Check for server errors

Report Section

When fuzzing is enabled, add this section to the test report:

## Form Fuzz Testing Results

### Summary
- **Inputs Tested**: 5
- **Payloads Tried**: 205
- **Vulnerabilities Found**: 2

### Critical Findings

| Input | Category | Payload | Result |
|-------|----------|---------|--------|
| #name | XSS | `<script>alert(1)</script>` | Executed |
| #search | SQLi | `' OR '1'='1` | Error 500 |

### XSS Tests (3 inputs)

| Input | Sample Payload | Result |
|-------|----------------|--------|
| #email | `<script>alert(1)</script>` | Sanitized |
| #name | `<script>alert(1)</script>` | **Executed** |
| #bio | `<img onerror=alert(1)>` | Sanitized |

### SQL Injection Tests (2 inputs)

| Input | Sample Payload | Result |
|-------|----------------|--------|
| #search | `' OR '1'='1` | **Error 500** |
| #id | `1; DROP TABLE--` | Rejected |

### Unicode Tests (5 inputs)

| Input | Sample Payload | Result |
|-------|----------------|--------|
| #name | `cafe n beijing` | Rendered OK |
| #bio | RTL markers | Layout OK |

### Length Tests (3 inputs)

| Input | Length | Result |
|-------|--------|--------|
| #email | 1K chars | Truncated (OK) |
| #bio | 10K chars | Accepted |
| #bio | 100K chars | **Client crash** |

### Recommendations

1. **[Critical]** Sanitize `#name` field - XSS vulnerable
2. **[Critical]** Fix SQL error handling in `#search` - reveals database info
3. **[Major]** Add length validation to `#bio` - crashes on large input

Integration with Personas

Fuzzing works alongside persona testing:

# Fuzz while testing as GenZ user
/user-test --url https://example.com/signup --persona genz-digital-native --fuzz

# Fuzz specific category
/user-test --url https://example.com/login --persona developer-critic --fuzz --fuzz-category xss

The persona still drives navigation and task completion, but form inputs are fuzzed when encountered.

Input Selection

Fuzz These Inputs

• <input type="text">
• <input type="email">
• <input type="password">
• <input type="search">
• <input type="url">
• <input type="tel">
• <textarea>
• <input type="hidden"> (if accessible)
• Rich text editors (contenteditable)

Skip These Inputs

• <input type="checkbox">
• <input type="radio">
• <input type="file">
• <input type="date/time">
• <select> dropdowns
• Disabled/readonly inputs

Best Practices

1. Start with --fuzz-category xss: Most common web vulnerability
2. Test staging, not production: Fuzzing can cause side effects
3. Combine with --record: Capture evidence of vulnerabilities
4. Use --json for CI/CD: Parse fuzz results programmatically
5. Test authenticated flows: Many vulnerabilities behind login

Limitations

1. Client-side only: Cannot detect server-side-only vulnerabilities
2. No blind injection: Time-based SQLi detection is limited
3. May trigger WAF: Fuzzing payloads can trigger security rules
4. State changes: Fuzzing may create test data in database
5. Rate limiting: May hit rate limits on aggressive testing

Severity Classification

Severity	Criteria	Example
Critical	Code execution, data exposure	XSS executed, SQLi data leak
Major	Application errors, crashes	Error 500, client crash
Minor	Poor handling, no security impact	Garbled unicode, no truncation
Info	Observations, potential issues	Long response time, verbose errors