idor-broken-object-authorization

SKILL: IDOR / Broken Object Level Authorization — Expert Attack Playbook

AI LOAD INSTRUCTION: IDOR is the #1 bug bounty finding. This skill covers non-obvious IDOR surfaces, all attack vectors (not just URL params), A-B testing methodology, BOLA vs BFLA distinction, chaining IDOR to higher impact, and what testers repeatedly miss.

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1. IDOR vs BOLA vs BFLA

Term	Meaning	Impact
IDOR	Insecure Direct Object Reference	Read/modify other users' data
BOLA	Broken Object Level Authorization (OWASP API Top 10 A1)	Same as IDOR, API terminology
BFLA	Broken Function Level Authorization	Low-priv user accesses HIGH-PRIV functions (e.g., admin endpoints)

Key distinction:

• BOLA = accessing object you shouldn't own (data belonging to other users)
• BFLA = accessing function you shouldn't be authorized for (admin CRUD operations, bulk actions, user management)

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2. WHERE TO FIND OBJECT IDs (ALL LOCATIONS)

Don't stop at URL path parameters — IDs appear in:

URL path:        GET /api/v1/users/1234/profile
URL query:       GET /orders?order_id=982
Request body:    {"userId": 1234, "action": "view"}
JSON fields:     {"resource": {"id": 5678, "type": "invoice"}}
Headers:         X-User-ID: 1234
                 X-Account-ID: 9999
Cookies:         user_id=1234; account=org_5678
GraphQL args:    query { user(id: "1234") { ... } }
Form fields:     <input name="documentId" value="5678">
WebSocket msgs:  {"event":"subscribe","channel_id":9999}

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3. A-B TESTING METHODOLOGY

The most systematic IDOR test approach:

Step 1: Create two test accounts: UserA and UserB
Step 2: Perform all actions as UserA, capture all requests
        (profile edit, order view, password change, file access, etc.)
Step 3: Note every object ID created or accessed by UserA
Step 4: Authenticate as UserB
Step 5: Replay UserA's requests using UserB's session token
Step 6: If UserB can read/modify UserA's data → BOLA confirmed

Victim matters: for real bugs, target existing users, not test accounts.
Report evidence: show UserA owns the resource, UserB accessed it.