Top 9 API Security Vulnerabilities: How to Defend Against Them

Understand the most common API vulnerabilities, how cybercriminals are targeting them and what you can do to prevent them.

Jun 11th, 2024 7:25am by Marco Palladino

Featued image for: Top 9 API Security Vulnerabilities: How to Defend Against Them

Featured image by Chris Linnett on Unsplash.

As APIs and microservices-based architectures have proliferated, the internet has quietly evolved into a global vehicle for API data exchange. Best estimates indicate that more than 70% of all internet traffic is now driven by APIs. As a result, this data exchange has become a tempting target for cyberattacks. It’s anticipated that API attacks will increase at a rate of 31% annually for the foreseeable future, costing hundreds of billions of dollars by the end of the decade. And attacks on APIs can be particularly devastating, potentially compromising proprietary and private data, disrupting service operations and eroding trust in brands and governments alike.

In this article, we explore nine of the most common API vulnerabilities seen today, how they’re being targeted by cybercriminals and how they can be addressed.

1. Excessive Data Exposure

Threat: Excessive data exposure happens when APIs unnecessarily expose sensitive data to clients, such as personal identifiers. An API will respond to a request with additional data that’s expected to be filtered or ignored by the user. This can occur through overly broad data retrieval operations.
Mitigation: Developers must implement strict output filtering to allow sharing only necessary data when an API responds to a request. Employing least-privilege or zero trust principles in data access can significantly reduce the risk of such exposures.

2. Broken User Authentication

Threat: Attackers assume other users’ identities, either by stealing login credentials or taking over user sessions. Broken user authentication strategies used to gain access include credential stuffing, where a known list of usernames and passwords is used to force a way in, unverified API endpoints that lack verification with CAPTCHA, or strategic password guesses to exploit any weak passwords.
Mitigation: Adopt multifactor authentication and conduct regular security audits to identify weak password policies, outdated authentication protocols or flawed token management. Regular updates will help to close any gaps in user authentication.

3. Broken Object-Level Authorization

Threat: Broken object-level authorization (BOLA) occurs when attackers access other users’ data by sending requests for data objects that should be protected with authorization controls. This can happen when access is granted without checking permissions or validating user identities.
Mitigation: Data access permissions need to be rigorously enforced across all API interactions to prevent unauthorized data access. Implementing strict access controls, such as role-based access control (RBAC) and attribute-based access control (ABAC), helps ensure that only authorized users can access specific data objects. An API gateway can help enforce these permissions by acting as a central point for managing and validating these access controls. Additionally, continuous monitoring and auditing of access logs can help detect and respond to unauthorized access attempts, further enhancing security.

4. Mismanagement in the API Ecosystem

Threat: Improper API asset management can expose businesses to significant security risks. Poorly cataloged or unmonitored APIs create vulnerabilities that attackers can exploit to access sensitive information or disrupt operations.
Mitigation: Regular reviews and updates to the API inventory to verify that all endpoints are known and secure are essential. This will help keep active APIs up to date, while deprecated APIs can be properly decommissioned.

5. Improperly Configured Rate Limits

Threat: Rate limiting is crucial for maintaining API performance and preventing abuse. Without effective rate limits, APIs can be overwhelmed by too many requests, leading to denial of service and making the system vulnerable to attacks. In some cases, attackers may intentionally consume an API’s resources to plummet its availability.
Mitigation: Implementing rate limiting not only helps traffic performance and management, it also protects APIs from automated attacks that can cause service degradation. Proper configuration of rate limits according to the application’s capacity and normal usage patterns is essential for maintaining service availability.

6. Broken Function-Level Authorization

Threat: Broken function-level authorization refers to scenarios where APIs don’t properly verify user permissions for specific operations, allowing unauthorized execution of functions. They can be targeted by intercepting application traffic, manipulating outward-facing code or pinpointing exposed endpoints.
Mitigation: API security strategies must include robust authorization checks that validate user permissions at every function call, thereby ensuring users can execute only the functions appropriate to their permission levels.

7. Code-Injection Attacks

Threat: Injection attacks occur when malicious inputs are sent to an interpreter as part of a command or query. APIs vulnerable to such attacks can execute unintended commands or access unauthorized data, significantly compromising system security.
Mitigation: To mitigate these risks, APIs should employ strict input validation and use prepared statements or parameterized queries in databases. Educating developers on secure coding practices is also vital to building resilience against injection vulnerabilities.

8. DDoS Attacks

Threat: Distributed denial of service (DDoS) attacks flood APIs with high volumes of requests to disrupt service. These attacks overwhelm an API’s resources, making it unable to respond to legitimate requests, which can lead to significant downtime and service interruptions. The implications of a successful DDoS attack can be severe, including loss of revenue, damaged reputation and potential breaches, especially if it’s combined with other attack vectors.

Mitigation: Effective mitigation involves sophisticated monitoring and response strategies to detect and neutralize these threats promptly. Employing rate limiting, geoblocking and challenge-response tests such as CAPTCHAs can help reduce the impact. Additionally, using cloud-based DDoS protection services can provide scalability to absorb and mitigate large-scale attacks, helping API services remain operational during an attack.

9. Outdated Security Models

Threat: Traditional security models often rely on a perimeter-based approach, which assumes that everything inside the network is trustworthy. However, this approach is vulnerable to insider threats and sophisticated external attacks that can breach the perimeter.

Mitigation: Zero trust security eliminates the concept of implicit trust within the network by continuously verifying every request, regardless of origin. By implementing zero trust principles, organizations can help ensure that only authenticated and authorized users and devices can access specific resources. This involves using technologies like mutual TLS (mTLS) for encryption and identity verification, micro-segmentation to isolate network segments, and continuous monitoring to detect and respond to threats in real time.

Ultimately, most API security risks are the result of poor API design, implementation or configuration, or upholding outdated security measures. However, these are all within our control. API gateways create a central entry point for all user API requests, making them the best way to ensure reliable API management.

For more API security insights, read our guide on becoming a secure API-first company.

Marco Palladino is an inventor, software developer and internet entrepreneur. As the CTO and co-founder of Kong Inc, he is Kong’s co-author, responsible for the design and delivery of the company’s products, while also providing technical thought leadership around APIs...