IDOR: The Sneaky Bug That Let Me See Everyone's Orders 🔓

Ever change a number in a URL and suddenly see someone else's data? Congrats, you found an IDOR! 🎉 (Please don't exploit it though.)

The "Oh Crap" Moment 😱

So there I was, testing a new feature on our e-commerce platform. Changed /orders/1234 to /orders/1235 in the URL just out of curiosity.

Result: I could see someone else's order. Their name, address, items, everything.

Then I tried /orders/1236. Another person's order.

My reaction: "Surely we validate this... right? RIGHT?!"

Narrator: They did not validate it.

In my experience building production systems, IDOR (Insecure Direct Object Reference) is one of the most common vulnerabilities I see. It's not flashy like SQL injection, but it's EVERYWHERE.

WTF is IDOR? 🤔

The fancy definition: When your app uses user-supplied input to access objects without proper authorization checks.

The real definition: Your app goes "Oh, you want order #1234? Here you go!" without asking "But are YOU the owner of order #1234?"

It's like a hotel giving you a room key just because you know the room number. No ID check, no reservation verification, nothing. 🏨

The Embarrassingly Simple Exploit 💀

The vulnerable code I found:

// Express.js - DON'T DO THIS
app.get('/api/orders/:id', async (req, res) => {
  const order = await Order.findById(req.params.id);

  // Just... sends it. No questions asked.
  res.json(order);
});

What a "hacker" does:

1. Log in with their own account
2. See their order: /api/orders/1234
3. Try /api/orders/1233, /api/orders/1232, etc.
4. Profit! They can now see everyone's orders. 💸

Damage potential:

• Personal information exposed
• Business data leaked
• Privacy laws violated (hello GDPR fines! 👋)
• Customer trust destroyed

As someone passionate about security, finding this in our own code was both terrifying and educational.

Real-World Examples That Made Headlines 📰

Bug bounty story from security communities:

A researcher found an IDOR in a major social media platform. By changing user IDs in API calls, they could:

• Read private messages
• Delete anyone's posts
• Access private profile data

Payout: $15,000 bounty. 💰

Another one: E-commerce site where changing /invoice/123 to /invoice/124 exposed other customers' invoices with full credit card details (last 4 digits, but still!).

These aren't sophisticated nation-state attacks. These are "change a number in a URL" level bugs.

How to Fix IDOR (The Right Way) ✅

1. Always Check Ownership 🔐

The secure version:

// Express.js - MUCH BETTER
app.get('/api/orders/:id', async (req, res) => {
  const order = await Order.findById(req.params.id);

  if (!order) {
    return res.status(404).json({ error: 'Order not found' });
  }

  // THE CRITICAL LINE 👇
  if (order.userId !== req.user.id) {
    return res.status(403).json({ error: 'Access denied' });
  }

  res.json(order);
});

Translation: "I found the order, BUT is it YOUR order? No? Get outta here!" 🚫

2. Laravel Makes This Easy 🎯

// Laravel - Built-in authorization
Route::get('/orders/{order}', function (Order $order) {
    $this->authorize('view', $order);

    return response()->json($order);
});

// In OrderPolicy.php
public function view(User $user, Order $order)
{
    return $user->id === $order->user_id;
}

Why I love this:

• Authorization is explicit
• Reusable across routes
• Throws 403 automatically if unauthorized
• One place to manage all access rules

In my 7+ years building APIs, Laravel's policy system has saved me countless times.

3. Use UUIDs Instead of Sequential IDs 🎲

The problem with sequential IDs:

/orders/1234
/orders/1235  ← Easy to guess!
/orders/1236

Better with UUIDs:

/orders/a3f8d7e2-4b9c-11ed-bdc3-0242ac120002
/orders/b7e9f3d4-4b9c-11ed-bdc3-0242ac120002  ← Good luck guessing!

Important: UUIDs are NOT security! They're obscurity. You STILL need authorization checks!

Think of it like this:

• Sequential IDs = numbered houses on a street
• UUIDs = random GPS coordinates in a forest

Both need locks on the doors, but one is harder to find.

Real Talk: Common IDOR Hiding Spots 🕵️

As someone from security communities, here's where we find IDOR most often:

1. API Endpoints (The Obvious One)

GET /api/users/123
PUT /api/profiles/456
DELETE /api/documents/789

2. File Downloads 📥

/download?file_id=1234
/reports/invoice_5678.pdf

I've seen systems where changing the file ID let you download OTHER PEOPLE'S FILES. Yikes!

3. Admin Panels (Double Yikes!) 🔥

/admin/users/edit/123
/admin/delete/order/456

Even "admin" routes need to check if THAT admin can modify THAT resource.

4. Hidden in POST Bodies 🙈

POST /api/update-email
{
  "user_id": 123,  ← Attacker changes this!
  "new_email": "[email protected]"
}

The fix: Use req.user.id from the session, NOT from the request body!

The Testing Checklist 📋

When I review code or do security testing, here's what I check:

For every endpoint that accesses a resource:

• Does it verify the user owns/can access this resource?
• What happens if I change the ID to someone else's?
• Does it check permissions BEFORE fetching data?
• Are authorization rules centralized (policies)?
• Do we log unauthorized access attempts?

Quick test:

1. Log in as User A
2. Get a resource ID for User A
3. Log in as User B
4. Try to access User A's resource

If it works? You have IDOR! 🚨

Pro Tips from the Trenches 💡

1. Fail Closed, Not Open

// BAD: Defaults to allowing access
if (user.hasPermission()) {
  // allow
}
// If permission check fails, what happens? Access granted!

// GOOD: Defaults to denying access
if (!user.hasPermission()) {
  return res.status(403).json({ error: 'Forbidden' });
}
// If permission check fails, access denied!

2. Don't Leak Information in Error Messages

// BAD: Tells attacker the resource exists
if (order.userId !== req.user.id) {
  return res.status(403).json({ error: 'This is not your order' });
}

// GOOD: Same response whether it exists or not
if (!order || order.userId !== req.user.id) {
  return res.status(404).json({ error: 'Order not found' });
}

If the attacker gets 403, they know the order exists. 404 keeps them guessing! 🎭

3. Use Middleware for Common Checks

// Create reusable ownership middleware
const checkOwnership = (Model) => async (req, res, next) => {
  const resource = await Model.findById(req.params.id);

  if (!resource || resource.userId !== req.user.id) {
    return res.status(404).json({ error: 'Not found' });
  }

  req.resource = resource; // Attach for route handler
  next();
};

// Use it everywhere
app.get('/orders/:id', checkOwnership(Order), (req, res) => {
  res.json(req.resource); // Already validated!
});

The Automated Testing Approach 🤖

In security communities, we often discuss automated IDOR testing:

// Jest/Mocha test
it('should not allow users to access other users orders', async () => {
  const userA = await createUser();
  const userB = await createUser();
  const orderA = await createOrder(userA.id);

  // Login as User B
  const tokenB = await loginAs(userB);

  // Try to access User A's order
  const response = await request(app)
    .get(`/api/orders/${orderA.id}`)
    .set('Authorization', `Bearer ${tokenB}`);

  expect(response.status).toBe(404); // Should be denied!
});

Run these tests in CI/CD. If they fail, someone broke authorization! 🚨

AWS Serverless? You're Not Safe Either! ☁️

Working with Lambda functions, I've seen this pattern:

// Lambda function - VULNERABLE
exports.handler = async (event) => {
  const orderId = event.pathParameters.id;

  // Gets order without checking ownership
  const order = await dynamoDB.get({
    TableName: 'orders',
    Key: { id: orderId }
  }).promise();

  return { statusCode: 200, body: JSON.stringify(order) };
};

The fix: Lambda authorizers + proper checks:

exports.handler = async (event) => {
  const orderId = event.pathParameters.id;
  const userId = event.requestContext.authorizer.userId; // From JWT

  const order = await dynamoDB.get({
    TableName: 'orders',
    Key: { id: orderId }
  }).promise();

  // Check ownership!
  if (!order || order.userId !== userId) {
    return {
      statusCode: 404,
      body: JSON.stringify({ error: 'Not found' })
    };
  }

  return { statusCode: 200, body: JSON.stringify(order) };
};

Tools to Find IDOR (Before Hackers Do) 🔧

From my experience in security research:

1. Burp Suite - Intercept requests, change IDs, see what happens
2. OWASP ZAP - Free automated scanner, finds low-hanging fruit
3. Postman - Test your APIs with different user tokens
4. Custom Scripts - Write scripts to test all your endpoints

Simple bash script to test:

#!/bin/bash
# Test orders endpoint with different IDs
TOKEN="your-jwt-token"

for id in {1000..1100}; do
  curl -H "Authorization: Bearer $TOKEN" \
       "https://api.yoursite.com/orders/$id" \
       -w "\nStatus: %{http_code}\n"
done

If you see 200 responses for IDs you shouldn't access? IDOR! 🎯

The Bottom Line 📌

IDOR is everywhere because:

1. It's easy to forget authorization checks
2. It's not caught by traditional security tools
3. Developers focus on authentication, not authorization
4. It requires testing from different user perspectives

Three rules to live by:

1. Never trust user input - Not even IDs in URLs
2. Always verify ownership - Every. Single. Endpoint.
3. Test with different users - What User A shouldn't see?

Think of it like this: Authentication is checking if you have a driver's license. Authorization is checking if you're allowed to drive THIS car. 🚗

You wouldn't let anyone with a license drive your car, right? Don't let anyone with a login access any data!

Quick Win Action Items 🏃‍♂️

Do this RIGHT NOW:

1. Pick your most sensitive endpoint (orders, messages, payments)
2. Try accessing it with a different user's ID
3. If it works, you have IDOR - FIX IT!
4. Add authorization checks to all resource endpoints
5. Write tests to prevent regression

Code review checklist:

For each endpoint:
- [ ] Fetches a resource by ID?
- [ ] Checks if current user owns/can access it?
- [ ] Returns 404 (not 403) for unauthorized access?
- [ ] Has tests for unauthorized access attempts?

---

Found an IDOR in the wild? Report it responsibly! Most companies have bug bounty programs. As someone passionate about security, I've seen researchers earn thousands for finding these bugs.

Want to learn more about API security? Hit me up on LinkedIn. In security communities, we love sharing war stories! 🛡️

Check out my code on GitHub - All my projects have proper authorization (learned the hard way! 😅)

Now go check your APIs for IDOR. I'll wait... ⏰🔒