Individual 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.
internal/tools/skills/data/web-application-security/exploiting-mass-assignment-in-rest-apis/SKILL.md
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- Last checked
- Nov 9, 2026
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- Nov 9, 2026
- License
- Apache-2.0
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- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- mass-assignment Declared skill tag
- api-security Declared skill tag
- privilege-escalation Declared skill tag
- rest-api Declared skill tag
- autobinding Declared skill tag
- parameter-injection Declared skill tag
- owasp-api Declared skill tag
- security Derived category
- security-application Derived category
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# 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
### How to CONFIRM a Hit (avoid false negatives)
- The positive signal is a **privileged field you injected actually PERSISTING** — not a 200 on the write. After sending the extra field, GET/re-read the object (or hit a privileged endpoint) and confirm the value changed: `role` is now `admin`, `isAdmin`/`verified` is `true`, `balance`/`price` reflects your value. The write succeeding while the field silently reverts is a false positive.
- Two-request proof, always: (1) baseline read shows the original value, (2) update with the injected field, (3) re-read shows it changed AND ideally a behaviour change (you can now reach an admin route, checkout at the lowered price, skip verification). Echoed-back-in-response is weaker than a re-read; an authorization effect is strongest.
- Discover the real field names first: diff the response body (which often exposes more fields than the request accepts) and use Arjun/param-miner — guessing one name and getting a 200 proves nothing.
- Do NOT conclude negative until you have tried ALL of these: