Troubleshooting Broken Object Level Authorization

Broken Object Level Authorization (BOLA) is the top API security risk according to OWASP. It happens when APIs fail to verify if users are authorized to access specific data objects, even if they are authenticated. This vulnerability can lead to data breaches, account takeovers, and compliance violations.

Key Takeaways:#

• What is BOLA? Attackers manipulate object IDs (e.g., changing /api/orders/123 to /api/orders/124) to access unauthorized data.
• Why it’s critical: BOLA is easy to exploit and affects APIs across industries like finance and healthcare.
• How to detect it: Look for APIs that accept object IDs without verifying user permissions or return 200 OK instead of 403 Forbidden for unauthorized access.
• How to fix it:
  • Enforce strict server-side authorization checks.
  • Use unpredictable identifiers like UUIDs instead of sequential IDs.
  • Validate API inputs and outputs using schemas.
  • Implement API gateways like Zuplo for centralized control and integrate security testing into CI/CD pipelines.

Quick Comparison: BOLA vs. Other Authorization Issues#

Next Steps#

1. Audit your APIs for BOLA vulnerabilities.
2. Use tools like OWASP ZAP or Burp Suite for automated testing.
3. Regularly monitor logs for suspicious activity, like sequential ID enumeration.
4. Educate your team on secure API development practices.

By addressing BOLA vulnerabilities, you protect sensitive data, ensure compliance, and maintain user trust.

How to Identify BOLA Vulnerabilities#

Warning Signs of BOLA Problems#

Spotting BOLA vulnerabilities early can save your system from major security breaches. One red flag is when APIs accept object identifiers without verifying them against the permissions of the logged-in user. For example, if an API endpoint behaves differently depending on the object ID passed - without returning an "unauthorized" error - it could be a sign of a BOLA issue.

Keep an eye out for APIs that return a 200 (success) response instead of a 403 (forbidden) code when unauthorized access is attempted. Also, watch for direct internal references in URLs, as these can indicate a potential vulnerability. If there are no internal checks to confirm ownership or permissions before delivering a response, the API is likely exposed to BOLA attacks.

These warning signs are just the starting point. Manual testing can dig deeper to reveal how your API handles manipulated object identifiers.

Manual Testing Methods for BOLA#

Manual testing remains one of the most effective ways to uncover BOLA vulnerabilities. By simulating various scenarios, you can see how your API reacts to manipulated inputs. Begin by examining API documentation or using tools like an interception proxy to find endpoints accepting object identifiers. Look for patterns in endpoints, such as /users/{userID} or /orders/{orderID}, that might indicate areas of risk.

A key method is to modify object identifiers in API requests and observe if unauthorized access is granted. For instance, consider this endpoint for a social media platform:

PATCH /api/users/profile
{ "userID": 12345, "displayName": "My New Name" }

If the API blindly trusts the provided userID without checking it against the logged-in user's session, an attacker could potentially change another user's profile.

"Broken Object Level Authorization occurs when an API fails to implement strict controls around who can access what. It's like leaving your house unlocked and hoping nobody with bad intentions walks in."

• StackHawk

GraphQL APIs require similar scrutiny. Test by altering object IDs in query parameters and check for vulnerabilities. Additionally, look for bulk access issues where the API might return data for multiple users instead of just the authenticated one.

For example, a healthcare system might have an endpoint like this:

GET /api/patients/{patientID}/records

If any authenticated user can access another patient’s records by simply changing the patientID, it reveals a severe flaw that compromises sensitive data. These examples show how small manipulations can lead to major security breaches, underlining the importance of thorough testing.

Automated BOLA Detection Tools#

While manual testing provides detailed insights, automated tools are essential for scaling your efforts across all endpoints. Traditional methods like fuzzing and static analysis often miss the nuances of BOLA vulnerabilities, but AI-powered tools can better interpret application logic and craft precise test cases.

Tools like OWASP ZAP and Burp Suite are popular choices for API security testing. OWASP ZAP is free and open-source, offering robust automation capabilities. On the other hand, Burp Suite provides broader functionality and greater flexibility, though its commercial pricing reflects these added features. Both tools can be adapted with add-ons for more advanced BOLA detection.

The effectiveness of automated tools is evident in real-world use cases. In 2023, researchers from Palo Alto Networks' Unit 42 used an AI-powered tool to test the Easy!Appointments platform. They discovered 15 BOLA vulnerabilities, tracked as CVE-2023-3285 through CVE-2023-3290 and CVE-2023-38047 through CVE-2023-38055. These flaws allowed low-privileged users to manipulate appointments created by higher-privileged users. The issues were patched in version 1.5.0.

Modern tools also excel at API discovery, identifying shadow or undocumented APIs that might otherwise go unnoticed. This capability is critical, especially as API-related cyberattacks continue to rise. For instance, India reported a staggering 3,000% increase in API attacks during Q3 of 2024, with over 271 million incidents in that period alone.

Automated tools can also integrate seamlessly into CI/CD pipelines, catching vulnerabilities early in the development process. Choose tools that provide actionable remediation advice instead of generic descriptions, as this helps developers address issues more efficiently.

When combined with manual testing, automated tools create a well-rounded strategy to tackle modern API security challenges effectively.

Broken Object Level Authorization (BOLA) Explained#

Here's a video that covers BOLA pretty well:

How to Fix BOLA Issues in APIs#

Fixing BOLA vulnerabilities requires a layered approach that combines strict access checks, input validation, and secure handling of identifiers. These steps help ensure that your API remains protected from unauthorized access and manipulation.

Setting Up Proper Object-Level Authorization#

The first step to addressing BOLA vulnerabilities is enforcing strict authorization on every API endpoint. This means verifying that the authenticated user has permission to access or modify the requested resource - not just confirming their identity.

Start by validating user permissions for every function that accesses a database record based on client input. Implement a centralized and reusable authorization mechanism to streamline this process.

"BOLA is already #1 on the OWASP API Security Top 10 list - and for good reasons. API providers do a great job at making sure that users are authenticated to the API, so they want to make sure that legitimate users have access. But the number one thing that's often overlooked is authorization, ensuring that user A can't access, interact with, or alter user B's resources - at all." - Corey Ball, Cybersecurity Consulting Manager and Author of "Hacking APIs"

To map users to their authorized resources, link user accounts with the specific objects they are allowed to access. For sensitive data, ensure every request verifies the user's association with the requested record.

Use a JWT token to extract the user ID instead of accepting it as a parameter. This prevents attackers from tampering with user identifiers in request parameters, as the user information comes directly from the authenticated session token.

Introduce robust session management systems and role-based access controls to enforce fine-grained permissions. This ensures users can only access data necessary for their roles or specific tasks. Additionally, implement schema validation to ensure your API processes only properly structured data.

Better API Schema Validation#

Strong authorization measures should be paired with API schema validation to guard against malicious inputs and unexpected behavior. By validating incoming data against predefined schemas, APIs can block harmful or malformed requests before they reach the application logic.

Define a JSON Schema for your API responses, detailing required fields, data types, and acceptable value ranges. For example, if your API expects a user ID, specify whether it should accept integers, UUIDs, or specific string patterns.

Integrate validation logic directly into your API using middleware or framework-provided libraries. This ensures incoming requests are checked against defined schemas before processing and outgoing responses comply with expected formats. Input validation helps block attackers from sending unexpected data, while output validation prevents accidental exposure of sensitive information.

Secure object identifiers by enforcing strict formatting rules and sanitizing inputs to reject special characters. When errors occur, return concise messages that inform the user without revealing system details. Regularly update your schemas to reflect changes in your API as it evolves.

Making Object Identifiers More Secure#

Even with strong authorization and validation, securing object identifiers is critical to reducing attack risks. Replace sequential IDs with UUIDs and map them to internal IDs. This approach makes external references unguessable while maintaining internal database efficiency.

For example, generate UUIDs when creating objects, store both the UUID and internal ID in your database, and use the UUID for all external API communications. This ensures that even if an attacker guesses an identifier, they cannot exploit it without proper authorization.

However, secure identifiers alone are not enough. Authorization checks remain essential - a valid UUID does not automatically grant access to a resource if the user is not authorized. A real-world example of this occurred when a major social media platform allowed users to access private images by altering the user_id parameter in a URL. This flaw exposed millions of users' personal photos until it was fixed.

To further minimize risks, apply the principle of least privilege. Limit user and system component permissions to only what is necessary for their roles or tasks. This reduces the damage an attacker can cause, even if they gain unauthorized access.

The urgency of addressing BOLA vulnerabilities cannot be overstated. In 2023, over 75% of reported API vulnerabilities stemmed from improper access control, with BOLA being the most exploited issue worldwide. Protecting your APIs from BOLA attacks is not optional - it’s a critical step for maintaining secure and trustworthy systems.

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Prevention and Best Practices#

To keep APIs secure, it’s essential to take proactive steps: enforce strict authorization controls, integrate continuous security testing, and monitor for potential threats. This layered approach not only complements earlier troubleshooting steps but also strengthens your API’s overall security.

Setting Up API Gateways for Authorization#

API gateways act as the frontline defense against BOLA (Broken Object Level Authorization) vulnerabilities. By centralizing security controls, they ensure consistent enforcement across every endpoint. Instead of embedding authorization logic into each individual microservice, gateways allow you to manage policies from one central location.

Zuplo's programmable API gateways make it easier to implement robust authorization measures. You can configure these gateways to validate JWT tokens, check OAuth scopes, and enforce role-based access controls before requests even reach your backend. For instance, if a user tries to access /api/invoices/12345, the gateway ensures they have the necessary permissions to view that invoice. This prevents attackers from exploiting endpoints by simply changing object IDs in their requests.

To enhance security further, use VPC Links to connect your gateway securely to private network applications. Pair this with fine-grained access control at the API level to double-check object ownership and user permissions, even after passing through the gateway.

But gateways aren’t the only tool in your arsenal. Automating security testing in your CI/CD pipeline is another key step.

Adding Security Testing to CI/CD Pipelines#

Integrating automated security tests into your CI/CD pipeline helps identify BOLA vulnerabilities early in development - before they ever reach production. This “shift-left” approach makes it easier and less expensive to tackle issues upfront. These automated tests build on earlier manual and automated testing methods, reinforcing a proactive stance on API security.

Tools like StackHawk allow teams to embed security testing directly into their CI/CD workflows. With every build, vulnerabilities are automatically scanned and flagged, with detailed reports that pinpoint the issue’s location in the code and suggest fixes.

Here’s how to set it up: configure your pipeline to run both SAST (Static Application Security Testing) and DAST (Dynamic Application Security Testing) tools on every commit. SAST tools analyze your codebase for security flaws, while DAST tools test the live application for vulnerabilities like BOLA. You can even write tests that simulate unauthorized access attempts to ensure your authorization mechanisms are rock-solid. If these tests fail, the build should stop immediately.

"A call to arms for CISOs: Stop chasing audits - embed end-to-end, automated API security testing throughout your SDLC to deliver fast, secure, and compliant product releases." – Aptori

Additionally, use IaC (Infrastructure as Code) vulnerability scanning to catch deployment misconfigurations that could lead to BOLA risks. Providing developers with tools that integrate directly into their IDEs can also encourage better authorization practices during API development.

Monitoring for Authorization Problems#

Real-time monitoring is essential for spotting BOLA attacks as they happen and uncovering security gaps. Effective monitoring goes beyond basic access logs by identifying patterns that hint at unauthorized access attempts.

Set up anomaly detection systems to flag unusual activity. For example, if a user suddenly accesses hundreds of customer records in a short period, it could signal a BOLA attack. Alerts should notify your security team immediately when such patterns arise.

Be on the lookout for sequential ID enumeration attacks, where attackers try different object IDs systematically (e.g., /api/users/1, /api/users/2, /api/users/3). Track these patterns and configure alerts for suspicious behavior.

Detailed logging is another critical tool. Record successful requests and failed authorizations, including user IDs, resources accessed, timestamps, and reasons for denial. This level of detail helps quickly identify and respond to attacks.

Dashboards can make monitoring more actionable. Use them to visualize key metrics like authorization failure rates, unusual access patterns, and frequently targeted endpoints. This allows your team to spot emerging threats at a glance.

To respond to detected threats, consider automating defensive actions. For instance, temporarily block IP addresses involved in enumeration attacks or require additional authentication for users exhibiting suspicious activity. Rate limiting at the gateway level can also slow attackers down, making their efforts more difficult and time-consuming. Finally, establish baseline behavior patterns for your API usage. If there’s a sudden spike in access or other unusual activity, it should trigger an immediate investigation.

Conclusion and Key Takeaways#

BOLA (Broken Object Level Authorization) has earned its spot as the #1 risk in the OWASP Top 10 API Security Risks for 2023. High-profile breaches in recent years highlight just how dangerous these vulnerabilities can be.

Key Lessons from Addressing BOLA#

Corey Ball, Cybersecurity Consulting Manager and author of Hacking APIs, puts it succinctly: "API providers do a great job at making sure that users are authenticated to the API, so they want to make sure that legitimate users have access. But the number one thing that's often overlooked is authorization, ensuring that user A can't access, interact with, or alter user B's resources - at all."

Three essential practices stand out when tackling BOLA:

• Server-side validation: Every object access request should be validated on the server side.
• Unpredictable identifiers: Use UUIDs or other non-sequential identifiers instead of easily guessable IDs.
• Least privilege principle: Restrict user permissions to only what is absolutely necessary.

Beyond improving overall security, addressing BOLA also helps meet regulatory requirements such as GDPR, CCPA, and HIPAA. This reduces the risk of privacy violations, account takeovers, financial fraud, or even sabotage of systems accessed via APIs.

These lessons provide the groundwork for the proactive security strategies discussed in the next section.

Next Steps for Strengthening API Security#

To build on these principles, consider the following actions to enhance your API security framework:

• Integrate continuous security testing: Use API audit and scanning tools directly within developers' IDEs to identify vulnerabilities early. This "shift-left" approach pairs well with both manual and automated testing.
• Session management and access control: Define user roles and permissions, bind object identifiers to authenticated sessions, and sanitize all inputs to prevent unauthorized access.
• Leverage API gateways: Tools like Zuplo act as centralized checkpoints for enforcing security policies across all endpoints. These gateways ensure consistent authorization controls and streamline policy management.

Additionally, conduct regular audits of access logs to spot enumeration attacks or unusual activity patterns. Pair this with routine penetration tests to uncover emerging vulnerabilities and reinforce your defenses. The ultimate goal? Building a security-first mindset where authorization is a priority from the start.

FAQs#

How can I protect my API from Broken Object Level Authorization (BOLA) vulnerabilities?#

To protect your API from Broken Object Level Authorization (BOLA) vulnerabilities, it’s crucial to enforce strict access controls for every object a user tries to access. Always verify that the user has the necessary permissions for the specific object mentioned in their request. Incorporating object-level security checks directly into your code is a must.

Another layer of protection comes from using unique, hard-to-guess identifiers for objects, which makes unauthorized access more difficult. Additionally, make it a habit to test your API for security weaknesses. Tools like OWASP ZAP and Burp Suite are excellent for conducting regular security assessments, helping you identify and address potential vulnerabilities before they become a problem. These steps are key to keeping sensitive data secure.

What are the best practices for securing server-side authorization to prevent unauthorized access?#

To maintain secure server-side authorization and guard against unauthorized access, it's crucial to incorporate authorization checks early in the development process. This approach ensures that roles and permissions are clearly outlined as your application grows. Using middleware to enforce authorization policies on every request is another essential step, as it helps to close off any unprotected endpoints.

Adopting the principle of least privilege is key. This means restricting user permissions to only what’s absolutely necessary for their specific role. One effective way to implement this is through role-based access control (RBAC). Beyond that, make it a habit to regularly review access logs to spot any unusual or suspicious activity. Adding multi-factor authentication (MFA) can also bolster security by requiring additional verification steps.

When combined, these measures create a reliable authorization framework that protects sensitive information and reduces the likelihood of unauthorized access.

How can I use tools like OWASP ZAP or Burp Suite to find and fix BOLA vulnerabilities in my API?#

Tools like OWASP ZAP and Burp Suite play a crucial role in identifying and resolving Broken Object Level Authorization (BOLA) vulnerabilities in APIs. These tools streamline the process of testing access controls by simulating unauthorized access attempts and analyzing how the API responds. This makes it easier to pinpoint areas where users might gain access to data or resources they shouldn’t.

With their active scanning features, you can detect misconfigurations and weaknesses in authorization checks. They also help validate object ownership, ensuring that proper access controls are enforced. This added layer of scrutiny helps protect sensitive data and reduces the risk of unauthorized access.