APIs sit at the core of modern applications, powering everything from mobile apps and SaaS platforms to cloud services, partner integrations, and internal microservices.
That growth has also positioned APIs among the most attractive targets for attackers.
In recent years, many high-profile breaches haven’t relied on sophisticated zero-day exploits, but on abusing poorly secured APIs.
A great example is the 2025 Stripe API campaign, where cybercriminals extracted thousands of payment card records by abusing legacy Stripe API integrations embedded in compromised websites.
With APIs becoming a primary attack surface, let’s explore the five most common mistakes that cyber teams make when implementing API security – and some tips on how developers and organizations can avoid these mistakes.
1. Weak or Missing Authentication
Authentication is the most fundamental security control for any API. Yet, recent research shows that it’s also the most commonly neglected, with nearly half (47%) of APIs skipping authentication altogether.
This means requests can be sent without verifying who or what is making them. It’s not that cyber teams don’t understand the importance of authentication. Usually, it’s a conscious tradeoff for the benefit of speed and convenience.
But taking these shortcuts introduces silent and serious exposure. It’s important to distinguish between no authentication, weak authentication, and improper token handling, as each introduces different risks.
No authentication means the API accepts and processes requests without any form of identity verification. Weak authentication is better, but still dangerous when it relies on static API keys, shared secrets, or long-lived credentials that are easy to bypass.
Improper token handling involves tokens that never expire or credentials used across multiple services. To address authentication issues, it’s best to apply modern mechanisms like OAuth 2.0 across all APIs.
Tokens should be rotated regularly and scoped to specific services and permissions to limit the blast radius in the event of exposure.
2. Broken Authorization
Broken authorization occurs when authentication is present, but the API doesn’t properly enforce what the user is allowed to access or do. It typically falls in one of two categories:
- Object-level authorization issues, when the API fails to verify ownership of a specific resource.
- Function-level authorization issues, when the API allows privileged or administrative actions without proper role checks.
Broken authorization is one of the most common and widely abused API security issues, and they allow attackers to escalate access using legitimate requests. It’s no coincidence that authorization failures dominate the OWASP API Top 10.
The problem usually stems from overreliance on client-side controls that can be easily bypassed, and the use of predictable object identifiers.
To prevent broken authorization, organizations should enforce server-side authorization checks on every request.
Additionally, authorization logic should be explicitly tested as part of API security testing, including negative testing scenarios that attempt to access unauthorized objects and privileged functions.
3. Excessive Data Exposure
Excessive data exposure is when API requests return more information than actually needed. It is usually caused by the assumption that sensitive fields will be filtered out on the client side.
While this simplifies development, it creates a risk in situations where attackers interact with the API directly and receive the full, unfiltered response.
Even if the API answers with only a subset of the data, attackers can easily inspect raw API responses to extract everything that’s returned.
This may include internal identifiers, personal data, account attributes, or metadata that was not intended to be visible to end users.
To avoid this issue, API responses should be designed with data minimization in mind. Teams should clearly define which fields are allowed to be returned for each endpoint and user role, rather than relying on generic or reusable response objects.
Sensitive fields should be masked or excluded entirely unless there is a clear and justified business need.
4. Lack of Rate Limiting and Abuse Controls
APIs that accept unlimited requests are the perfect candidates for abuse. Without effective rate limiting, attackers can launch all sorts of attacks, including credential stuffing, brute-forcing, DDoS, and data scraping.
In most cases, basic rate limiting does exist, but is applied broadly and relies too heavily on IP-based thresholds, which attackers can easily bypass via their bot infrastructure that includes rotating IPs and proxies.
To be truly effective, organizations can apply endpoint-specific rate limits that reflect the sensitivity and expected usage of each API operation. Identity controls tied to users, tokens, and service accounts are also necessary beyond IPs.
5. No Visibility into API Traffic
In most environments, APIs generate zero-to-none security logging, making it impossible for IT teams to identify malicious activity.
Even if logging exists, it may lack the relevant security context to detect abuse, such as who is making the request, what data is being accessed, or whether the action was successful.
This issue can arise even with organizations that prioritize logging but have no inventory of all internal, partner, and legacy APIs they need to monitor.
At a minimum, logs should capture the caller identity (user, service, or token), the endpoint accessed, the action performed, and the outcome of the request.
These logs can feed into a Security Information and Event Management (SIEM) system where analysts can easily access them alongside other security telemetry.
Final Thoughts
API breaches are growing alongside API adoption, and they rarely happen because attackers discover something entirely new.
As seen in most API-related incidents, attackers succeed by exploiting the same repeatable security gaps, whether it’s a weak third-party integration, or missing authentication checks.
The good news is that these mistakes are largely preventable.
The main obstacle is educating developers about the security implications of API design and implementation decisions, and how essential security controls must become a baseline, rather than optional add-ons.
