# Testing API For Mass Assignment Vulnerability

> Use when tests APIs for mass assignment (auto-binding) vulnerabilities where clients can modify object properties they should not have access to by including additional parameters in API requests. The tester identifies writable endpoints, adds undocumented fields to request bodies (role, isAdmin, price, balance), and checks if the server binds these to the data model without filtering. Part of OWASP API3:2023 Broken Object Property Level Authorization.

- Skill: `oyi77/testing-api-for-mass-assignment-vulnerability` (Agent Skill)
- Install (CLI): `npx skillmds add oyi77/testing-api-for-mass-assignment-vulnerability`
- Raw SKILL.md: https://api.skillmd.com/api/skills/oyi77/testing-api-for-mass-assignment-vulnerability/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- License: Apache-2.0
- Author: oyi77 (https://skillmd.com/u/oyi77)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/oyi77/testing-api-for-mass-assignment-vulnerability

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# Testing Api For Mass Assignment Vulnerability

## Overview

Cybersecurity skill for testing api for mass assignment vulnerability. Follows industry best practices and security standards.

## When to Use
**Trigger phrases:**
- "testing api for mass assignment vulnerability"
- "Tests APIs for mass assignment (auto-binding) vulnerabilities where clients can "


- Testing API endpoints that accept JSON/XML request bodies for user profile updates, registration, or object creation
- Assessing whether the API binds all client-supplied properties to the data model without an allowlist
- Evaluating if users can set privileged attributes (role, permissions, pricing, balance) through regular update endpoints
- Testing APIs built with ORMs that auto-bind request parameters to database models
- Validating that server-side input validation restricts writeable properties per user role

**Do not use** without written authorization. Mass assignment testing involves modifying object properties in potentially destructive ways.


## When NOT to Use

- When you lack proper authorization for testing
- For production systems without change management
- When the task requires legal or compliance expertise beyond technical scope


## Prerequisites

- Written authorization specifying target API endpoints and scope
- Test accounts at different privilege levels
- API documentation or OpenAPI specification to identify expected request fields
- Burp Suite Professional for request interception and parameter injection
- Python 3.10+ with `requests` library
- Knowledge of the backend framework (Rails, Django, Express, Spring) to predict parameter binding behavior

## Workflow

```python
# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text) for k, v in IOC_PATTERNS.items()}
```

1. **Reconnaissance** — Gather information about the target related to api. Identify attack surface.
2. **Vulnerability Identification** — Enumerate potential api weaknesses using automated and manual techniques.
3. **Exploit Development/Selection** — Use mass assignment vulnerability to identify and test api vulnerabilities.
4. **Execution** — Execute the api test in a controlled manner with proper authorization.
5. **Post-Exploitation** — Document the impact and extent of successful exploitation.
6. **Reporting** — Write detailed findings with reproduction steps, impact assessment, and remediation guidance.

## Tools

- **mass assignment vulnerability** — Primary tool for this skill
- **Vulnerability Scanner** — Automated weakness identification
- **Exploitation Framework** — Controlled exploitation testing
- **Reporting Tool** — Findings documentation and tracking


## Process

1. **Reconnaissance** — Gather target information, identify attack surface, enumerate services
1. **Analysis/Exploitation** — Execute the technique, analyze results, document findings
1. **Reporting** — Document IOCs, write findings, provide remediation recommendations

## Verification

- [ ] All api procedures executed completely and documented
- [ ] Findings validated against multiple data sources
- [ ] False positives identified and filtered
- [ ] Results documented with evidence and timestamps
- [ ] Recommendations provided with risk-based prioritization

## Anti-Rationalization Table

| Rationalization | Reality |
|---|---|
| "We are too small to be targeted" | Automated attacks target everyone. Size does not matter. |
| "Security slows us down" | A breach slows you down 100x more. Build security in from the start. |
| "We will fix it after launch" | Vulnerabilities in production are exploited within hours. Fix before deploy. |