Broken object-level authorization (BOLA) is the most widely exploited API vulnerability because it is simple for attackers to use and easy for development teams to overlook. A single unchecked object identifier in an API request can expose sensitive data across users, accounts, or entire systems. This guide explains what BOLA is, how attackers exploit it, why it is so dangerous across modern API architectures, and how organizations can detect and prevent it at scale using accurate, low-noise security testing.

Key takeaways

• BOLA is the most common and impactful API vulnerability because it exposes sensitive data through simple identifier manipulation.
• Attackers often only need to change an object ID to access another user’s data, especially when identifiers are predictable.
• Effective prevention requires consistent server-side authorization checks for every request across every API endpoint.
• Accurate automated testing is essential for finding BOLA early and at scale, especially in distributed and fast-changing API environments.
• Invicti speeds up detection and reduces noise by validating real BOLA vulnerabilities with proof-based scanning so you can prioritize and remediate issues with confidence.

What is BOLA?

Broken object-level authorization (BOLA) occurs when an API exposes direct object identifiers without verifying if the requester is allowed to access the referenced object. When an endpoint accepts identifiers such as user IDs or record keys, it should check access permissions on every request. If the API omits that verification step, attackers may be able to access or manipulate data by replacing the identifier with another valid one.

BOLA leads the OWASP API Security Top 10 because APIs naturally operate on object IDs. Unlike application frontends that often hide identifiers behind forms, APIs reveal the underlying structure, so using predictable identifiers makes that structure easy to explore. BOLA is present whenever an API returns data solely because the identifier matches a valid record, regardless of requester authorization.

BOLA is the API-specific case of insecure direct object references (IDOR), focused on the failure to validate object-level permissions. Both issues arise when identifiers are exposed and authorization is not enforced on the server.

How attackers exploit BOLA vulnerabilities

Attackers typically exploit BOLA by modifying object identifiers in API calls and observing how the system responds. If they can access another user’s data by incrementing an ID or swapping a reference, there could be BOLA there. Predictable or sequential identifiers encourage enumeration because attackers can script requests to brute-force access and harvest data at scale.

Microservices can unintentionally widen the attack surface. Teams may assume that adjacent or upstream services have already performed authorization, which leaves downstream endpoints unprotected if they haven’t. When this happens across multiple services, a single request can bypass intended controls and reach sensitive data. 

A simple BOLA example

To understand how BOLA manifests in code, consider what happens when this legitimate API request arrives:

GET /api/v1/accounts/12345
Authorization: Bearer <token-for-user-A>

The request itself is perfectly valid: user A is authenticated with a proper bearer token and is requesting account number 12345. Let’s see how this request can be processed insecurely (resulting in BOLA), and then securely. For both examples, we’ll assume the application has already successfully authenticated user A based on the bearer token.

The vulnerable implementation with BOLA

@app.route('/api/v1/accounts/<account_id>')
def get_account(account_id):
    account = db.query(Account).filter(id=account_id).first()
    return jsonify(account)

This basic code never checks whether user A is authorized to access account 12345 specifically. It simply queries the database for the requested account ID and returns the data if it exists.

An attacker can exploit this just by changing the identifier and sending:

GET /api/v1/accounts/12346
Authorization: Bearer <token-for-user-A>

If the API returns account 12346 that user A shouldn’t have access to, the endpoint has a BOLA vulnerability.

The secure implementation without BOLA

@app.route('/api/v1/accounts/<account_id>')
def get_account(account_id):
    user_id = get_current_user_id_from_token()
    account = db.query(Account).filter(
        id=account_id,
        owner_id=user_id
    ).first()
    
    if not account:
        return jsonify({"error": "Account not found"}), 404
    
    return jsonify(account)

The secure version extracts the user ID from the authenticated token, then queries the database with both the account ID and the owner ID. This ensures the account exists and belongs to the requesting user. If either condition fails, the API returns a 404 error rather than exposing unauthorized data.

This server-side authorization check must happen on every request, regardless of how the API is accessed. Note that using UUIDs or other non-sequential identifiers doesn’t prevent BOLA but merely makes enumeration harder – authorization logic is always required.

Why BOLA is so dangerous in APIs

BOLA is dangerous because it offers immediate access to sensitive data with little effort. Many APIs reveal internal structures that are not visible in traditional app interfaces, so a single missing check may expose an entire dataset.

The compliance implications are significant. Unauthorized access to customer records, financial data, or health information can trigger obligations under GDPR, HIPAA, PCI DSS, and other frameworks. Related incidents often require public disclosure, lead to regulatory penalties, and damage customer trust.

Modern service-based architectures also increase the likelihood of BOLA. Internal and shadow APIs may evolve rapidly, and teams may overlook authorization while focusing on feature delivery. These endpoints often handle privileged operations and can be more vulnerable than public-facing APIs.

How to detect BOLA vulnerabilities

Detecting BOLA isn’t obvious because it requires evaluating authorization behavior, not just checking for functional responses. To do this through automated API security testing, you need to probe endpoints with both valid and manipulated identifiers to confirm whether an API enforces access control consistently.

Accurate detection also requires understanding multi-step workflows. Some APIs make authorization decisions based on earlier requests, session state, or chained operations. Effective testing validates object access at every step.

Predictability in identifiers presents another risk. Sequential IDs, weak GUIDs, and similar patterns help attackers guess valid identifiers. Automated testing that explores these patterns can uncover issues earlier in development.

Manual testing has been the traditional way of finding BOLA simply because an experienced pentester can quickly see BOLA opportunities and explore them. However, manual testing alone rarely provides complete coverage due to the many places that object identifiers can appear. Automated scanning applied already in CI/CD pipelines helps to ensure consistent and repeatable verification across all environments.

How to prevent and fix BOLA

Prevention begins with enforcing object-level authorization on every request. Secure API design should assume that exposed identifiers can be manipulated and you need to verify authorization on the server side. Client-side controls, naming conventions, or obscured identifiers cannot replace real access checks.

Using opaque or indirect identifiers is useful to make enumeration harder, but it still requires robust authorization logic. Scope-based permissions and least-privilege design strengthen the boundary around each object and limit what authenticated users can reach.

Proper logging and monitoring practices help detect unusual access attempts, such as sequences of identifier probes or unexpected cross-account queries. This visibility supports both early detection and post-incident analysis.

Business and compliance impact of BOLA

BOLA-related breaches often expose sensitive customer data. This leads to direct compliance impacts, from mandatory breach notifications to regulatory penalties. Beyond legal exposure, organizations face reputational damage that can slow customer acquisition and erode long-term trust.

Large-scale remediation also introduces operational cost. Development teams must pause planned work to go back and address security gaps, which for BOLA can require redesigning or rearchitecting services to implement proper access controls.

How Invicti detects BOLA

API scanning on the Invicti platform can automatically detect two BOLA variants:

• Horizontal BOLA, where users can access objects belonging to other users with the same privilege level. This is the “regular” BOLA case.
• Vertical BOLA, where users can access objects belonging to users with a different (higher) privilege level. This is the more severe variant of BOLA that may allow unauthorized access to admin-only resources.

Invicti’s API vulnerability scanner detects BOLA using proof-based scanning that validates real exploitability. Instead of generating large volumes of theoretical findings, Invicti confirms many types of vulnerabilities and provides evidence that the issue is genuine. This reduction in noise helps security teams prioritize actual risks and accelerates remediation.

Multi-step and stateful API scanning allows Invicti to evaluate authorization across complex workflows rather than treating each request in isolation. This capability uncovers bypasses that occur only when specific sequences of API calls are made.

Invicti’s API discovery features help find undocumented or forgotten endpoints where BOLA vulnerabilities are more likely. When used alongside Invicti’s application security posture management (ASPM) capabilities, this gives organizations a centralized view of potential authorization issues across their entire API footprint.

Next steps for securing your APIs from BOLA

BOLA remains so common and impactful because it is easy for attackers to exploit and easy for devs to miss. Fortunately, it is also preventable when developers enforce consistent authorization checks in securely designed APIs and organizations use accurate, automated testing to validate those checks. With proof-based scanning and comprehensive API testing on the Invicti platform, teams can eliminate BOLA vulnerabilities before they become incidents.

See how Invicti automatically detects and validates BOLA vulnerabilities in APIs at scale – schedule a demo today.