It wasn’t a complex SQL injection or a tricky deserialization flaw. It was a failure to ask one simple question: “Are you really authorized to modify that object?”

Every hacker knows the feeling: that moment when a simple, almost trivial input causes a cascade of unintended, catastrophic events on a production system. I recently found myself in that sweet spot while auditing a major corporate portal, leading to one of the cleanest Insecure Direct Object Reference (IDOR) vulnerabilities I’ve ever seen.

This vulnerability didn’t just expose user data — it allowed any basic user to take over the identity, contact details, and designation of internal employees, including management and HR.

The Subtle Leak That Handed Me the Keys

But the xid not guessable so easily.

So, my first target was the application’s user validation logic. Most sites have an API that checks if an email exists for a “Forgot Password” function. This portal’s endpoint was promisingly named: /api/v1/user/checkAccountExist.

I started probing with public emails, and I could guess that it is so easy because of the contact us page (almost 50+ employees’ emails in my hand): [[email protected]](mailto:[email protected]), [[email protected]](mailto:[email protected]).

And that’s where the developer made their first critical mistake.

When I hit a valid email, the API didn’t just say “Yes, this account exists.” Instead, it generously included the user’s primary key — the xid. This unique identifier is the application's direct object reference to the profile.

I didn’t need to guess. I didn’t need brute force. By checking a few known corporate emails, I had instantly and silently generated a verified list of high-value internal employee xids. I now had the victims' coordinates.

The Easiest Escalation I’ve Ever Seen

With my victim’s xid notes (let's call it VICTIM_99999), I moved to the main event: the Profile Update section.

1. I logged in with my account.
2. I opened my own profile settings and changed my name to “Tester.”
3. I intercepted the request in Burp Suite.

The request body, intended to update my profile, looked perfectly innocent:

{
  "name": "Tester",
  "mobileNumber: "323232323",
  "company": "ccccccc",
  "designation": "Researcher",
  // ... other update fields
}

Now, the chilling part. The server was clearly trusting the xid parameter provided in the POST request to decide who to update. The authentication token in the header proved I was logged in, but the server never checked if the token’s owner (MY_XID_12345) matched the body’s target (MY_XID_12345).

The Bypass: I simply deleted my own ID and inserted the CEO/HR/CISO's xid I had just enumerated.

Field Original Value (My Profile) to New Value (CEO’s Profile)”

xid”"MY_XID_12345" to "VICTIM_99999"

"name""Tester" to "Evil Impersonator"

"mobileNumber""1234..." to "9990001112"

“company”: “dddddddddd”,

“designation”: “CEO/HR/CISO”,

and so on.......

I hit Forward.

Result: Instant Success. HTTP 200.

I had just leveraged my privilege session to update the profile of a CEO/HR/CISO’s. The changes were immediate and persistent. I could log out and verify that the employee’s official details (through the CEO/HR/CISO’s user name that leaked in response)— Name, Contact Number, Company Affiliation — were all now fraudulent.

What Trusting the Client Costs You

This is the quintessential IDOR scenario, packaged neatly with a perfect enumeration vector. The impact wasn’t just “data exposure;” it was identity corruption.

Imagine an attacker changing the phone number of the Head of HR on the official portal and then calling employees, pretending to be them. The potential for large-scale social engineering and internal fraud is immense.

The Developer’s Golden Rule:

If you are building an API that modifies an object, NEVER, EVER rely on the object reference (like xid) provided by the client's payload.

1. Retrieve the User ID: Get the authenticated user’s ID only from the secure session token (JWT payload, Session Store). This ID is your source of truth.
2. Ignore the Client ID: Discard or ignore the xid provided in the request body. If the user is updating their own profile, the ID from the session is the only ID you need.

This vulnerability was a masterclass in why we should trust our session state and treat all client input as hostile. It’s a vivid reminder that sometimes, the most sophisticated attacks exploit the most simplistic coding oversights.