APIs quietly handle some of the most important work in modern applications. They process requests, share data, and connect services every second. Because they work in the background, API security is often overlooked, until a breach exposes sensitive data or disrupts critical systems.
That’s where the OWASP API Security Top 10 comes in. It acts as a practical guide that highlights the most common and dangerous API security failures. In this blog, we’ll walk through the key API risks covered by OWASP and explain why they matter, so you can better protect your applications, data, and users before attackers find the gaps.
The OWASP API Security Top 10 highlights the most common failures that attackers look for when targeting APIs. Understanding these risks helps teams spot weaknesses early and build APIs that protect data, users, and core business systems.
1. Broken Object Level Authorization (BOLA)
BOLA happens when an API does not properly check whether a user is allowed to access a specific piece of data. An attacker can change an ID in an API request and see or modify someone else’s data.
Why it matters: This often leads to direct data exposure, which is one of the most common causes of API breaches.
2. Broken Authentication in APIs
APIs fail at authentication when they don’t properly verify who is making the request. This could be due to weak tokens, missing checks, or poor session handling.
Why it matters: Attackers can take over user accounts or act as trusted users.
3. Excessive Data Exposure
Sometimes APIs return more data than needed, relying on the client to filter it. Even if the UI hides the data, attackers can still see it in the API response.
Why it matters: Sensitive information like personal data or internal details can leak easily.
4. Lack of Resource and Rate Limiting
When APIs don’t limit how often requests can be made, attackers can overload the system or brute-force credentials.
Why it matters: This can lead to denial-of-service attacks, account abuse, or high infrastructure costs.
5. Broken Function Level Authorization (BFLA)
BFLA occurs when an API does not properly restrict access to certain actions. A normal user may be able to perform admin-level functions.
Why it matters: Attackers can change settings, delete data, or gain higher privileges.
6. Mass Assignment Vulnerabilities
This happens when APIs automatically bind user input to internal objects without proper filtering. Attackers can modify fields they should not control.
Why it matters: It can lead to privilege escalation or unauthorized data changes.
7. Security Misconfiguration in APIs
APIs may expose unnecessary endpoints, use default settings, or lack proper security headers.
Why it matters: Misconfigurations make it easier for attackers to discover and exploit weaknesses.
8. Injection Attacks in API Endpoints
APIs that don’t properly validate input can be tricked into running malicious commands or queries.
Why it matters: Injection attacks can expose data or fully compromise backend systems.
9. Improper Assets Management
Organizations often forget to remove old API versions or test endpoints. These outdated APIs remain accessible and unsecured.
Why it matters: Attackers target these forgotten assets because they are easier to exploit.
10. Insufficient Logging and Monitoring
When APIs don’t log activity properly, attacks go unnoticed. Teams may not know a breach happened until it’s too late.
Why it matters: Delayed detection increases damage, recovery time, and compliance risk.
Impact of API Security Failures
When an API is exposed, the impact goes far beyond technical issues. Attackers can bypass applications entirely and interact directly with business systems. The result is lost revenue, compliance issues, customer churn, and long-term brand damage, often before leadership even knows an attack is happening.
Common impacts of API security failures include:
- Data breaches and data leaks: Exposed APIs can reveal personal, financial, or confidential business data, leading to loss of customer trust and legal trouble.
- Compliance and regulatory penalties: API breaches often violate data protection laws, resulting in fines, audits, and increased regulatory scrutiny.
- Financial losses: Downtime, incident response, legal costs, and lost customers can have a direct impact on revenue.
- Service disruption and downtime: Attacks such as abuse or denial-of-service can make APIs unavailable, affecting applications and customers.
- Damage to brand reputation: Public security incidents reduce customer confidence and can take years to recover from.
- Increased operational workload: Security incidents force teams to shift focus from innovation to crisis management and recovery.
By understanding these impacts, organizations can better appreciate why securing APIs is critical to protecting both technology and the business.
Best Practices to Prevent OWASP API Security Risks
Preventing API security issues doesn’t require complex solutions. Most OWASP API risks can be reduced by following clear, consistent security practices from the start. The key is to treat APIs as critical business assets, not just technical endpoints.
Here are some practical best practices that help reduce common API security risks:
- Apply strong authentication and authorization: Always verify who is calling the API and what they are allowed to do. Check permissions at both the user level and the object level for every request.
- Limit data exposure: Return only the data that is required for each request. Avoid sending sensitive or unnecessary fields in API responses.
- Use proper rate limiting: Control how often an API can be called to prevent abuse, brute-force attacks, and service disruption.
- Validate all inputs: Never trust data coming into an API. Validate, sanitize, and filter inputs to prevent injection and mass assignment attacks.
- Secure API design from the start: Build security into the API design phase. Clearly define access rules, data flows, and error handling before development begins.
- Keep APIs and dependencies updated: Remove unused endpoints, deprecate old API versions, and regularly update third-party libraries to reduce exposure to known vulnerabilities.
- Harden configurations: Disable default settings, hide debug information, and ensure APIs use secure headers and encryption.
- Maintain an accurate API inventory: Know which APIs exist, who owns them, and which versions are active. Forgotten APIs are easy targets for attackers.
- Enable logging and monitoring: Track API activity and set alerts for unusual behavior. Early detection helps limit damage and speed up response.
- Test APIs regularly: Perform security testing and penetration testing focused on OWASP API Security Top 10 risks to identify issues before attackers do.
By following these best practices, organizations can significantly reduce API security risks and build APIs that are safer, more reliable, and easier to manage over time.
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We don’t just find issues, we explain the business impact, prioritize risks, and provide clear remediation guidance. With Peneto Labs, you gain better visibility into your API security posture and the confidence to protect your applications, data, and customers.
Conclusion
APIs play a critical role in how modern applications work, which also makes them a prime target for attackers. Many API security failures don’t happen because of advanced attacks, but because of missing controls, weak design choices, or lack of visibility. The OWASP API Security Top 10 helps teams clearly understand where these risks exist and how they are commonly exploited.
Strengthening API security starts with awareness and continues with consistent action. By following OWASP guidelines, applying secure design practices, and testing APIs regularly, organizations can reduce exposure and protect sensitive data.
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