BOPLA: Why Protecting the Object ID Isn't Enough (Broken Object Property Level Authorization) š
BOPLA: Why Protecting the Object ID Isn’t Enough (Broken Object Property Level Authorization) š
In the rapidly evolving landscape of API security, developers have finally begun to master the art of the “ID check.” Most modern applications now verify that User A cannot access User B’s private data simply by changing a user_id in a URLāa vulnerability known as BOLA (Broken Object Level Authorization).
However, a more insidious threat has emerged, one that bypasses standard ID-level checks and targets the very attributes that define an object. Welcome to the world of BOPLA (Broken Object Property Level Authorization).
Ranked as API3:2023 in the OWASP API Security Top 10, BOPLA represents the next frontier of API vulnerabilities. It is no longer enough to ask, “Can this user see this object?” Security teams must now ask, “Can this user see or change these specific fields within the object?”
This article provides a comprehensive deep dive into BOPLA, exploring its origins, its mechanicsāspecifically Mass Assignment and Excessive Data Exposureāand how you can secure your APIs against the sophisticated attacks of 2025 and 2026.
1. The Evolution: From BOLA to BOPLA
To understand BOPLA, we must first understand its predecessor. BOLA (formerly IDOR) occurs when an application provides access to an object based on a user-supplied ID without verifying if the user has the right to access that specific record.
BOPLA (Broken Object Property Level Authorization) is the granular sibling of BOLA. It occurs when an API allows a user to access or modify specific properties of an object that should be restricted, even if the user has legitimate access to the object itself.
The OWASP Merger
In the 2023 update of the API Security Top 10, OWASP merged two previous categoriesāExcessive Data Exposure (API3:2019) and Mass Assignment (API6:2019)āinto a single, unified category: BOPLA.
The reasoning was simple: both vulnerabilities stem from the same root causeāa failure to validate authorization at the property level rather than just the object level.
2. Why “Object-Level” Security is Failing
Imagine a digital banking API. A user, Alice, logs in and requests her account details: GET /api/v1/accounts/12345.
Object-Level Check (BOLA): The server checks if Account 12345 belongs to Alice. It does. Access granted.
Property-Level Check (BOPLA): The server returns the JSON object. However, instead of just returning her balance and account_name, it returns the entire database row, including internal_credit_score, is_premium_member, and anti_fraud_flags.
Alice now knows her internal credit rating and fraud statusādata she was never meant to see. This is Excessive Data Exposure.
Now consider the reverse. Alice wants to update her display name. She sends a PATCH request:
{
"display_name": "Alice The Great",
"internal_credit_score": 850
}
If the backend blindly updates every field provided in the JSON body, Alice has just hacked her own credit score. This is Mass Assignment.
In both cases, the Object ID check passed, but the Property Level Authorization failed.
3. The First Pillar: Excessive Data Exposure (The Read Leak)
Excessive Data Exposure happens when an API relies on the client (the frontend) to filter data. Developers often find it easier to send the “full object” from the database to the frontend, assuming that if the UI only displays the username, the other fields (like password_hash or ssn) are safe.
The “Hidden” Dangers
Hackers don’t use your UI. They use tools like Burp Suite, Postman, or Insomnia to inspect the raw JSON response.
Common Scenarios in 2025:
The User Object Trap: An API for a social media app returns the full User object when you click on a profile. While the UI only shows a bio, the JSON contains
last_login_ip,email_verified_status, and abackup_email.The IoT Leak: Smart home APIs often return technical metadata, including Wi-Fi SSIDs and internal device tokens, which can be leveraged for lateral movement within a network.
The PII Goldmine: A 2025 research study into S&P 500 companies revealed that many “AutoSwagger” (automated API documentation) tools accidentally exposed internal-only fields in their schemas, leading to massive PII (Personally Identifiable Information) leaks.
Real-World Impact
When an API returns hashed passwords, even if they are salted, it provides an attacker with a “dictionary attack” target. If it returns internal roles, it gives an attacker a roadmap for privilege escalation.
4. The Second Pillar: Mass Assignment (The Write Hack)
Mass Assignment is the “write” side of BOPLA. It occurs when an application automatically binds client-provided data to internal data models without a strict “allow-list.”
Modern web frameworks (like Ruby on Rails, Spring Boot, and Express.js) make development fast by allowing “Object-Relational Mapping” (ORM). A single line of code can take a JSON body and save it directly to the database.
The Exploit Mechanism
An attacker probes the API by adding “guessed” properties to a request.
Input: PATCH /api/users/me
Legitimate Body: {"bio": "Hello world"}
Attacker’s Body: {"bio": "Hello world", "role": "admin", "is_verified": true}
If the developer used a generic update function like User.update(req.body), the attacker has successfully promoted themselves to an administrator.
Mass Assignment in the Wild: The “is_admin” Property
In a famous historical case, a researcher found they could become an admin on GitHub by adding an admin: 1 parameter to a public-key upload request. While GitHub fixed this years ago, the logic persists in thousands of modern microservices today.
5. Technical Deep Dive: Vulnerable vs. Secure Code
Let’s look at how this manifests in a typical Node.js/Express environment using an ORM like Mongoose or Sequelize.
ā The Vulnerable Way (Mass Assignment)
app.patch('/api/profile/update', async (req, res) => {
const user = await User.findById(req.user.id);
// VULNERABLE: Blindly assigning all properties from req.body to the user object
Object.assign(user, req.body);
await user.save();
res.json(user); // ALSO VULNERABLE: Excessive Data Exposure (returns full object)
});
In this snippet, an attacker can send {"is_premium": true} or {"account_balance": 99999} and the database will update accordingly.
ā The Secure Way (Property-Level Authorization)
const _ = require('lodash');
app.patch('/api/profile/update', async (req, res) => {
const user = await User.findById(req.user.id);
// SECURE: Only allow specific, non-sensitive fields to be updated (Allow-listing)
const allowedUpdates = _.pick(req.body, ['bio', 'display_name', 'profile_picture']);
Object.assign(user, allowedUpdates);
await user.save();
// SECURE: Only return necessary fields to prevent data exposure
const publicProfile = _.pick(user, ['id', 'username', 'bio', 'display_name']);
res.json(publicProfile);
});
6. BOPLA in 2025: The Rise of AI and Auto-Discovery
The threat of BOPLA has intensified due to two major trends:
1. Automated API Discovery Tools
Tools like AutoSwagger and Param Miner are now more sophisticated. Attackers use them to scan for “hidden” parameters. By analyzing the naming conventions of an API (e.g., if there is a first_name, there is likely a last_name), AI-driven fuzzed requests can discover sensitive fields like internal_notes or partner_id that developers forgot to hide.
2. GraphQL Introspection
GraphQL is particularly prone to BOPLA. Because GraphQL allows users to “ask for exactly what they want,” a lack of field-level authorization can allow a user to query for sensitive fields they shouldn’t access. If your GraphQL schema doesn’t have strict @auth directives on individual fields, you are effectively “BOPLA-vulnerable” by design.
7. Business Impact of BOPLA
BOPLA isn’t just a technical “bug”; it’s a significant business risk.
Data Breaches: Even if you don’t lose the whole database, leaking thousands of email addresses or SSNs via Excessive Data Exposure triggers mandatory reporting under GDPR and CCPA.
Financial Fraud: In Fintech, Mass Assignment can lead to unauthorized credit increases, fee waivers, or “VIP” status acquisition without payment.
Reputational Damage: Nothing erodes user trust faster than a “logic flaw” that allows any user to see private account settings or change their own permissions.
8. How to Prevent BOPLA: The Ultimate Developer Checklist
Securing your API against Property Level Authorization issues requires a “Shift Left” mentalityāsecurity must be part of the design phase, not an afterthought.
1. Implement Strict DTOs (Data Transfer Objects)
Never map your database models directly to your API. Create a separate class or interface (a DTO) for every request and response.
- Input DTO: Defines exactly which fields the API will accept.
- Output DTO: Defines exactly which fields the API will return.
2. Use Allow-lists (Never Block-lists)
When updating an object, explicitly define which fields are “safe.”
- Bad: “Ignore the role and id fields.”
- Good: “Only accept the phone_number and address fields.”
3. Avoid “ToJSON” Automation
Be careful with methods like .toJSON() or JSON.stringify(object). In many frameworks, these methods serialize the entire object. Instead, use specialized serializers (like ActiveModel::Serializers in Ruby or Jackson Views in Java) to filter out sensitive properties.
4. Field-Level Authorization Logic
For sensitive fields (like is_admin or subscription_tier), implement a secondary check.
Pseudo-code: if (req.body.role && !currentUser.is_superuser) { return 403; }
5. Disable Introspection in Production
For GraphQL and Swagger/OpenAPI, disable introspection and public schema access in production environments to prevent attackers from “mapping” your object properties.
6. Automated Testing (DAST)
Use Dynamic Application Security Testing (DAST) tools that specifically look for mass assignment. Modern tools will take a valid POST request and attempt to add common administrative fields (like admin, role, is_staff) to see if the server accepts them.
9. Testing for BOPLA: A Mini-Guide for Pentesters
If you are a security researcher or QA engineer, here is how you can hunt for BOPLA:
Analyze Responses: Capture a GET request. Look for fields that aren’t shown in the UI. Are there internal IDs? Hashed values? Booleans like
is_internal?The “Guess and Check” Update: Find a PUT or PATCH endpoint. Try adding a field found in a GET response that you shouldn’t be able to change.
Example: If the GET returns "is_verified": false, try sending a PATCH with "is_verified": true.
Parameter Polarity: If you see a field like
notifications_enabled: true, try sending its opposite or a related guess likeadmin_access: true.Check Older Versions: Sometimes v2 of an API is secure, but v1 (still active) remains vulnerable to Mass Assignment.
10. Conclusion: Security is in the Details
As we move through 2026, the complexity of APIs will only grow. The shift from BOLA to BOPLA signifies a move toward more granular, logic-based security.
Protecting the Object ID is the “entry fee” for API securityāit’s the bare minimum. True protection comes from understanding the data lifecycle of every single property in your application. By implementing DTOs, strict allow-listing, and robust property-level authorization, you ensure that your API doesn’t just open the right door, but only allows guests to see the right rooms.
Key Takeaway: In API security, Less is More. Every extra property you return in a JSON response is a potential leak, and every unvalidated property you accept is a potential hack. Keep your payloads lean, your whitelists tight, and your authorization granular.