**Broken Object Level Authorization (BOLA)** is the top API security risk
according to [OWASP](https://owasp.org/). 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
| **Issue** | **Description** | **Example** |
| ------------------------------------------------------------------------------- | ----------------------------------------------------------------- | --------------------------------------- |
| **BOLA** | Unauthorized access to specific data objects by manipulating IDs. | Changing `/api/orders/123` to `/124`. |
| [**BFLA**](./2025-07-30-troubleshooting-broken-function-level-authorization.md) | Accessing endpoints users should not have access to at all. | Accessing admin-only APIs. |
| **BOPLA** | Accessing unauthorized properties within an object. | Viewing hidden fields in API responses. |
### Next Steps
1. Audit your APIs for BOLA vulnerabilities.
2. Use tools like [OWASP ZAP](https://www.zaproxy.org/) or
[Burp Suite](https://portswigger.net/burp) for automated testing.
3. Regularly monitor logs for suspicious activity, like sequential ID
enumeration.
4. Educate your team on
[secure API development practices](https://zuplo.com/blog/2022/12/01/api-key-authentication).
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](https://www.stackhawk.com/product/)
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](https://zuplo.com/docs/articles/testing-api-key-authentication).
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](https://www.paloaltonetworks.com/)'
Unit 42 used an AI-powered tool to test the
[Easy!Appointments](https://easyappointments.org/) 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](./2025-07-31-api-discoverability-why-its-important-the-risk-of-shadow-and-zombie-apis.md)
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](./2025-04-15-how-api-schema-validation-boosts-effective-contract-testing.md)
to ensure your API processes only properly structured data.
### Better API Schema Validation
Strong authorization measures should be paired with
[API schema validation](https://zuplo.com/blog/2022/03/18/incoming-body-validation-with-json-schema)
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](https://zuplo.com/docs/policies/acl-policy-inbound), 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.
## 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](https://zuplo.com/docs/policies/open-id-jwt-auth-inbound), check
OAuth scopes, and
[enforce role-based access controls](./2025-01-28-how-rbac-improves-api-permission-management.md)
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.