Every minor security gap is an opportunity for an attacker. And when you ignore API security, it leaves a critical gap in an organization’s defenses, because APIs are the primary attack surface for modern applications.
They act as a direct pipeline to backend systems and data. So, neglecting them leads to the same operational, financial, and legal fallout as any major security failure – just faster, and with less warning.
The scale of API attacks is so high, that 99% of organization reported an API-related security incident in the past 12 months.
Also, the risks fall into three categories – data breaches and exposure, system vulnerabilities and abuse, and business/compliance fallout. And here, each one is mapped to the OWASP API Security Top 10.
1: Data Breached and Exposure
Excessive Data Exposure (OWASP API3)
Many APIs return the full backend object and rely on the frontend to filter what a user actually sees. Call the API directly and you can often pull the raw, unfiltered data, such as PII, financial details, credentials. And these was never meant to reach the client. OWASP folded this into API3 in its 2023 update, alongside mass assignment.
Broken Object-Level Authorization (BOLA) (OWASP API1 — #1 on the list)
An attacker changes an ID in a request, such as an order ID, an account number, a user ID and pulls back someone else's private data, because the API never checked whether this caller was allowed to access that specific object. It requires no advanced tooling, which is exactly why it remains the most exploited API flaw year after year.
2: System Vulnerabilities and Abuse
Broken Authentication / Account Takeover (OWASP API2)
Weak or misconfigured tokens, such as reused API keys, long-lived JWTs, loosely configured OAuth flows let attackers hijack real sessions or forge new ones.
- 52% of 60 major API breaches analyzed in 2025 traced back to broken authentication
- 59% of known API vulnerabilities require no authentication at all to exploit
- Only 21% of security teams say they can reliably detect an attack at the API layer (Wallarm, 2025–2026)
Resource Exhaustion / DDoS (OWASP API4: Unrestricted Resource Consumption)
Without rate limiting, scripted requests can overwhelm servers, causing downtime or a runaway cloud bill. This risk climbed from the 7th-ranked API threat in 2024 to 4th in 2025, driven by automated scraping and enumeration attacks that are now far easier to run at scale.
Injection Attacks (now folded into OWASP API10: Unsafe Consumption of APIs)
Unvalidated input lets attackers inject SQL or script payloads to manipulate the backend directly, or run unauthorized commands. OWASP moved this under API10 because injected input increasingly travels through a chain of trusted API calls rather than a single form field.
Shadow / Zombie APIs (OWASP API9: Improper Inventory Management)
It’s the risk most other blogs underweight Old, undocumented, or "temporary" endpoints stay live in production after a newer version ships, skipping every security review the documented APIs went through.
- Typically, 30–40% of an organization's total API footprint
- Only 15% of organizations report strong confidence in their own API inventory
3: Business and Compliance Fallout
Regulatory Fines
A breach traced to a neglected API can violate GDPR, HIPAA, PCI DSS, or sector-specific rules and regulators treat an exposed API the same as any other data-handling failure.
The cost backs this up: the global average data breach now runs 4.99 million in the U.S., which is an all-time high, driven partly by regulatory penalties and slower detection (IBM).
Supply Chain / Third-Party API Risk
Payment gateways, analytics SDKs, map providers, AI model endpoints. A compromise anywhere in that chain becomes your incident if the integration wasn't security-reviewed.
This is a bigger driver than most teams assume: 27% of 2025 API breaches were caused by unsafe consumption of third-party APIs, the second largest root cause after broken authentication.
Reputational Loss
Trust, once broken by a data leak, is slow and expensive to rebuild but often costing years and a real share of the customer base, regardless of how fast the technical fix lands. It's harder to pin to a single stat, but it consistently shows up in breach cost research as a compounding, long-tail cost that outlasts the incident itself
The Bottom Line
Every risk above traces back to one root cause: a lack of continuous visibility into what APIs exist, who's calling them, and whether each call is actually authorized. Closing the gap takes three things:
- Continuous API discovery, including the undocumented, shadow ones.
- Authentication-first hardening, since broken auth alone accounts for over half of major breaches.
- Behaviour-based monitoring to catch misuse, not just malformed traffic.
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