We tend to hear a lot about API vulnerabilities, between the OWASP Top 10 API Security Vulnerabilities and CISA’s Known Exploited Vulnerabilities Catalog. 42Crunch also recently published research on the most common API vulnerabilities, highlighting broken authentication, broken authorization, and misconfigurations as widespread issues.

While industry analysis demonstrates which API vulnerabilities are most common, we tend to hear less about which types of vulnerabilities are the most harmful or have the most negative consequences. This makes it slightly harder to rank the top API risks you should watch out for within your systems.

Of course, no API vulnerability is a good vulnerability, but that doesn’t mean all API vulnerabilities are created equal, either. With that in mind, we’ve put together a list of the five most disastrous API vulnerabilities you need to watch out for.

1. Broken Object Level Authorization (BOLA)

Broken object-level authorization (BOLA) is the single most disastrous API vulnerability, as it turns authentic API traffic into a vector for a potential data breach. Malicious attackers only have to manipulate an object ID from an authenticated API response to request sensitive data from other users. These can be anything from medical records to admin resources to invoices, without having to use a single piece of malware or write a single line of code.

For these reasons, BOLA is a highly exploited API vulnerability. It’s especially insidious as it’s virtually identical to authenticated traffic. This means traditional API monitoring and security tools and techniques won’t catch it.

2. Business Logic Abuse

Business logic abuse has become one of the most damaging API vulnerabilities as it turns the official API logic against itself. Instead of writing malicious code or taking advantage of code execution bugs, attackers exploit flaws in sequencing, rate limiting, rules around pricing, entitlement checks, refund systems, loyalty programs, or approval workflows to gain access to a system.

By exploiting business logic gaps, malicious attackers can commit fraud, steal data, manipulate inventory, or escalate their privileges without being detected by traditional cybersecurity systems, as the traffic appears to be legitimate. For example, an Uber user was able to generate $50,000 in free rides using a legitimate promo code.

3. Authentication and Token Abuse

You might be starting to notice a pattern. Like both BOLA and business logic abuse, JSON Web Tokens (JWTs) and OAuth-related API vulnerabilities let attackers impersonate legitimate users. Ineffective JWT validation, leaked API keys, intercepted tokens, improper redirects, and exposed tokens can give attackers the key to the kingdom without ever having to breach the system.

Once they’ve got an authenticated token, malicious actors are often able to access microservices, cloud-based systems, and other sensitive services. This is particularly dangerous, as more and more organizations are exposing business functions through APIs instead of traditional web applications, making compromised API credentials and tokens more of a risk. The risk of token abuse is also a danger in AI-related workflows.

4. Server-Side Request Forgery (SSRF)

Server-side request forgery (SSRF) is one of the most dangerous API vulnerabilities because it allows a simple web request to compromise an organization’s internal infrastructure. SSRF flaws let cyberattackers force a server to make requests to internal services, cloud-based endpoints, Kubernetes-based APIs, internal admin resources, or protected network resources. In cloud-based environments, SSRF is the first step toward stolen credentials, unauthorized lateral movement, or full infrastructure takeover. The increase of AI agents, integrations, and webhooks makes SSRF even more risky, as it creates a wider surface area.

5. Remote Code Execution Through API Integrations

Remote code execution (RCE) is one of the most severe API vulnerabilities, as it can result in an attacker stealing credentials, installing ransomware, attacking supply chains, or even taking over the server completely. RCE flaws are less common than authentication vulnerabilities, but their impact can be much more severe. To make matters worse, this vulnerability can be exploited by AI systems connected via API integration, as well as plugin ecosystems, CI/CD integrations, and agentic frameworks that are able to execute code.

Consider the case of MOVEit, where attackers were able to exploit an API vulnerability that made it possible to execute code remotely that installed web shells in hundreds of organizations around the world, resulting in sensitive information being exposed from millions of users. Cases like this demonstrate the severity of API vulnerabilities that enable RCE.

Why Disastrous API Vulnerabilities Require Extra Attention

When talking about API security, it’s easy to get caught up on which vulnerabilities occur most often. Yet, frequency and impact aren’t the same thing. Some vulnerabilities might rarely, if ever, happen, yet they can have disastrous results. As IBM notes in 2025’s Cost of a Data Breach Report, the average cost of a data breach in the United States is $10.22 million in maintenance and investment costs, legal costs, and expenses related to notifying your existing customers.

The most disastrous API vulnerabilities can cause large-scale data breaches, escalated privilege, compromised infrastructure, ransomware, or financial fraud. Many of them exploit authorized methods, too, which makes them doubly dangerous. For highly API-driven organizations, it’s another reminder that you need to employ additional cybersecurity methods like identity-based access control and systems trained to detect anomalous behavior or traffic.