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Introduction
A seemingly harmless profile update request, a single tampered `customer_id` parameter, and no server-side verification: this is the recipe for a critical account takeover that researcher “Razzle Mouse” recently uncovered in a private travel booking platform. The vulnerability is a classic Broken Access Control flaw from the OWASP Top 10, combined with an Insecure Direct Object Reference (IDOR), which allowed the attacker to overwrite any user’s profile data—email, name, and more—without any interaction from the victim, leading to a full account takeover (ATO). This silent but devastating attack vector highlights a persistent security gap in modern web applications, even those handling sensitive customer data like flight itineraries and payment details.
Learning Objectives
- Understand how a combination of Broken Access Control and IDOR in profile update functionality can lead to a silent account takeover.
- Learn to manually exploit such flaws using Burp Suite, including how to identify, modify, and re-send vulnerable API requests.
- Acquire the knowledge to automate IDOR enumeration and implement robust, server-side authorization checks to prevent such critical vulnerabilities.
You Should Know
- Manual Exploitation: From Profile Update to Full Account Takeover
Step-by-Step Guide
This vulnerability was discovered in a profile update feature. The core mistake was trusting a client‑supplied `customer_id` without verifying if the authenticated user actually owned that resource.
- Step 1: Environment Setup & Account Creation
For safe testing, create two separate accounts on the target platform: - Attacker Account: `[email protected]` → `customer_id: 217`
– Victim Account: `[email protected]` → `customer_id: 218` - Step 2: Intercept the Legitimate Request
Log in as the attacker and navigate to the Profile Update section. Enable Burp Suite proxy (e.g.,127.0.0.1:8080) and intercept the request when updating the profile. The original request might look similar to:
POST /api/v1/profile/update HTTP/1.1
Host: target.com
Authorization: Bearer [bash]
Content-Type: application/json
{
"customer_name": "Attacker",
"customer_email": "[email protected]",
"customer_id": 217
}
- Step 3: Modify the Critical Parameter
In Burp Suite’s Repeater tab, change the `customer_id` from the attacker’s value (217) to the victim’s value (218) while keeping the attacker’s JWT token intact:
{
"customer_name": "Attacker",
"customer_email": "[email protected]",
"customer_id": 218
}
- Step 4: Submit the Modified Request
Send the modified request. A `200 OK` response indicates the server processed the update without validating that the attacker owns the victim’s profile. The victim’s email address and name are now silently overwritten with the attacker’s data. -
Step 5: Confirm Account Takeover
Since the victim’s email was changed to the attacker’s email, the attacker can: - Initiate a password reset for the victim’s account; the reset link will be sent to the attacker’s email.
- Log in directly using the attacker’s email and the newly set password.
- Gain full access to the victim’s sensitive data, including flight itineraries, travel history, invoices, and saved payment methods.
2. Automating IDOR Enumeration with Burp Suite Extensions
Manual testing is essential, but to scale the hunt for broken access controls, you can automate IDOR detection using Burp Suite extensions.
Step-by-Step Guide
- Step 1: Install the Autorize Extension
In Burp Suite, navigate to the Extensions tab, then BApp Store. Search for “Autorize” and install it. This extension automates authorization tests by replaying requests with different user sessions. -
Step 2: Configure User Accounts
Set up two user accounts in the target application: a low-privilege user and a high-privilege user (e.g., administrator). Configure Autorize with the respective session cookies or tokens for each role. -
Step 3: Configure the Extension
In the Autorize tab:
- Set the Low-privilege Cookie (attacker’s session).
- Set the High-privilege Cookie (victim’s session or another target).
-
Select the desired authorization check method (e.g., “Enforce” to detect if a low-privilege user can access a high-privilege endpoint).
-
Step 4: Browse the Application
Use Burp Suite’s proxy to browse the application while logged in as the low-privilege user. Autorize will automatically replay each request using the high-privilege cookie and compare the response statuses and lengths to identify potential access control violations. -
Step 5: Analyze the Results
Review the Autorize results panel. Requests that return a `200 OK` or similar success status when replayed with a different user’s session are strong indicators of a broken access control flaw. The tool will highlight endpoints where the low-privilege user was able to access data or perform actions meant for the high-privilege user.
3. Vulnerability Mitigation: Implementing Robust Server-Side Access Controls
Based on the OWASP Authorization Cheat Sheet, the following principles are critical to prevent this class of vulnerability.
Step-by-Step Guide for Developers & Security Teams
- Step 1: Deny by Default and Enforce Least Privilege
Implement a default-deny policy for all access control decisions. Explicitly grant access only to specific users or roles for well-defined resources. Never rely on client-side parameters (e.g., JavaScript, hidden form fields) for authorization decisions; all checks must be performed on the server for every request. -
Step 2: Use Indirect Object References
Instead of exposing direct database keys (e.g.,customer_id) to the client, use a server-side mapping layer. Generate a random, unguessable reference (like a UUID) for each resource. The application then maps this indirect reference to the actual database key internally, making it impossible for an attacker to guess a valid identifier for another user. -
Step 3: Validate Resource Ownership on Every Request
For every endpoint that accesses or modifies a resource, the server must verify that the currently authenticated user has the appropriate permissions (e.g., ownership or role-based access). This check should be performed after authentication and before any data is retrieved or modified. -
Step 4: Implement Rate Limiting & Monitoring
Enforce strict rate limiting on sensitive endpoints like profile updates and password resets to mitigate automated IDOR enumeration attacks. Additionally, log all failed access attempts and set up alerts for anomalous patterns, such as rapid changes to the `user_id` parameter across multiple requests from a single session.
4. Commands & Tools for Penetration Testing
Here is a curated list of practical commands and tools to help you identify and exploit broken access control vulnerabilities.
- Linux / macOS Commands for API Testing
Using `curl` to test for IDOR by modifying the `user_id` parameter:
Authenticate and capture session token
TOKEN=$(curl -s -X POST https://target.com/api/login \
-H "Content-Type: application/json" \
-d '{"username":"attacker","password":"P@ssw0rd"}' | jq -r '.token')
Attempt to access another user's profile using a modified ID
curl -X GET "https://target.com/api/user/profile?user_id=218" \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json"
Attempt to update another user's email
curl -X PUT "https://target.com/api/user/profile" \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{"user_id": 218, "email": "[email protected]"}'
- Automated Tools for IDOR/BA Testing
-
Autorize: A Burp Suite extension for automated authorization tests.
- Auto-IDOR-Hunter: A passive Python-based Burp extension that uses 12 distinct bypass techniques to hunt for IDOR and BOLA vulnerabilities.
- IDOR-Scanner: A Burp extension that automates detection and enumeration of vulnerable numeric fields.
- Arjun: A tool to discover hidden HTTP parameters, which can be used to find unlinked IDOR parameters in API endpoints.
Example: Install and run Arjun to find hidden parameters git clone https://github.com/s0md3v/Arjun.git cd Arjun python3 arjun.py -u https://target.com/api/user/profile --get
5. Training Courses & References
To build deeper expertise in identifying and preventing broken access controls, the following courses and resources are recommended:
- OWASP: Broken Access Control (Pluralsight) – Learn to recognize, test, and prevent the most critical access control weaknesses.
- OWASP Top 10 – A01:2021 – Broken Access Control (NICCS) – Hands-on lab environment for identifying, exploiting, and offering remediation advice.
- PortSwigger Web Security Academy (Access Control Labs) – Free, interactive labs covering IDOR, privilege escalation, and multi-step access control flaws.
- GitHub: Broken-Access-Control_lab – A hands-on CTF-style lab for Node/Express covering IDOR, vertical privilege escalation, JWT abuse, and batch authorization bypass.
- OWASP Authorization Cheat Sheet – The definitive guide for implementing robust authorization logic.
What Undercode Say
- The core lesson is that trusting client‑side parameters for authorization is a fatal design flaw that enables silent, complete account takeover.
- Automated enumeration and robust, server‑side ownership checks are the most effective defenses against this class of vulnerability.
In the travel booking platform case, the impact was significant because the attack was completely silent: the victim never received any notification that their profile email had been changed. This allowed the attacker to quietly take over accounts and access sensitive data like flight itineraries and payment details. The responsible disclosure process was swift, but many applications still leave such endpoints vulnerable due to a lack of server-side validation. For penetration testers, this case reinforces the need to test every endpoint that references a resource identifier, even seemingly low-risk ones like profile updates. For developers, it is a clear mandate to enforce the “deny by default” principle and never rely on client-supplied IDs for authorization.
Prediction
- -1 A single broken access control flaw in a popular travel booking platform could expose millions of user accounts to silent takeover, potentially leading to massive identity theft and financial fraud.
- -1 Attackers are increasingly automating IDOR enumeration using AI-powered Burp extensions, making large-scale exploitation faster and harder to detect without robust rate limiting.
- -P The emergence of AI-assisted security testing tools will eventually help developers automatically detect and patch such flaws during the CI/CD pipeline, shifting left on security.
- -1 The travel industry remains a high-value target; as more OTAs adopt API-first architectures, the attack surface for broken access controls will continue to expand.
- -P Regulatory bodies may soon mandate third-party penetration testing for broken access controls in sectors handling PII, similar to PCI DSS for payment data.
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