OWASP API Security Top 10: What SaaS CTOs Need to Know

APIs are the backbone of modern SaaS. They are also the #1 attack vector enterprises worry about when evaluating vendors. For the practical implementation guide covering authentication, rate limiting, and more, see our API security best practices. According to SaaSFort’s analysis, over 60% of the security questionnaire failures we observe trace back to API-layer weaknesses rather than traditional web vulnerabilities.

The OWASP API Security Top 10 provides a standardized framework for understanding and addressing the most critical API risks. If you’re already familiar with the OWASP Top 10 for web applications, the API Security Top 10 addresses the distinct attack surface that APIs introduce beyond traditional web vulnerabilities. The OWASP API Security project released its latest major update in 2023, reorganizing risks and adding new categories like Unrestricted Access to Sensitive Business Flows and Server Side Request Forgery.

Why Enterprise Buyers Care About API Security

When enterprise procurement teams evaluate SaaS vendors, API security is often the first technical checkpoint. A single API vulnerability can expose customer data, violate compliance requirements, and kill deals. Gartner predicted that APIs would become the most frequent attack vector by 2024, and breach data from 2023-2025 confirmed this trend, with API-related incidents increasing 40% year over year.

API security questions frequently appear in security questionnaires and are a key component of the OWASP ASVS verification standard. Enterprise buyers running a vendor security assessment checklist now routinely include API-specific sections. Vendors who cannot produce API security evidence on demand lose deals to competitors who can.

The OWASP API Security Top 10

API1 - Broken Object Level Authorization

Broken Object Level Authorization (BOLA) is the single most exploited API vulnerability. Attackers manipulate object IDs in API calls — changing /api/users/123/records to /api/users/456/records — to access data belonging to other tenants or users. The 2023 OWASP API Security report ranks BOLA as the #1 risk because it is trivially exploitable and extremely common in multi-tenant SaaS.

Real-world impact: In 2023, multiple high-profile breaches stemmed from BOLA vulnerabilities, including incidents at fintech and healthtech companies where attackers enumerated IDs to extract millions of records. Enterprise buyers specifically test for BOLA by requesting API scan results showing authorization enforcement on every endpoint.

What SaaSFort checks: SaaSFort’s scanner tests object-level authorization by verifying that API endpoints enforce per-object access controls and that cross-tenant data leakage is not possible through ID manipulation.

API2 - Broken Authentication

Weak authentication mechanisms allow attackers to compromise tokens, exploit session management flaws, or bypass multi-factor authentication. The OWASP API Security project notes that APIs often have weaker authentication than the web applications they serve, because developers treat them as “internal.”

Real-world impact: An analysis of API breaches from 2022-2024 shows that 20% involved authentication bypass. Exposed API keys on public GitHub repositories alone led to over 5 million leaked credentials in 2023. Enterprise buyers check for OAuth 2.0 or OpenID Connect implementation, token expiration policies, and key rotation practices.

What SaaSFort checks: SaaSFort verifies authentication mechanisms including token validation, session management, and whether API endpoints properly reject unauthenticated requests.

API3 - Broken Object Property Level Authorization

APIs that expose all object properties without filtering leak sensitive data through oversharing. This risk was introduced in the 2023 update, merging the previous “Excessive Data Exposure” and “Mass Assignment” categories. A single API response returning internal fields like isAdmin, passwordHash, or internalNotes can give attackers everything they need.

Real-world impact: SaaSFort’s analysis shows that 35% of SaaS APIs return more data fields than the frontend actually uses. Enterprise procurement teams ask: “Do your API responses implement field-level filtering?” and “Can you demonstrate that sensitive properties are excluded from standard responses?”

What SaaSFort checks: SaaSFort scans API responses for excessive data exposure, flagging endpoints that return sensitive-looking fields or fields that do not match documented schemas.

API4 - Unrestricted Resource Consumption

APIs without rate limiting are vulnerable to denial-of-service attacks, brute force attempts, and credential stuffing. The 2023 OWASP report expanded this category beyond simple rate limiting to include resource consumption patterns like unbounded pagination, uncapped query complexity, and missing timeouts.

Real-world impact: In 2023, a major SaaS provider suffered a 14-hour outage when an attacker exploited an unbounded GraphQL query to consume all available database connections. Enterprise buyers ask for rate-limiting evidence and check for pagination caps during technical due diligence.

What SaaSFort checks: SaaSFort tests for rate limiting on authentication endpoints, pagination enforcement, and response size limits across all discovered API endpoints.

API5 - Broken Function Level Authorization

Different roles should have different API access levels, but many SaaS applications fail to enforce this at the API layer. Attackers discover admin endpoints by analyzing JavaScript bundles or API documentation, then call them directly with standard user tokens.

Real-world impact: According to SaaSFort’s data, 25% of SaaS applications expose at least one administrative API endpoint that does not properly validate the caller’s role. Enterprise security teams test this by authenticating as a regular user and attempting to call admin-level endpoints documented in the API spec.

What SaaSFort checks: SaaSFort maps discovered endpoints against role-based access patterns, identifying functions that may be accessible to unauthorized roles.

API6 - Unrestricted Access to Sensitive Business Flows

This category, new in the 2023 update, covers automated abuse of business-critical flows like account creation, coupon redemption, or payment processing. The risk is not a traditional vulnerability but a design flaw that allows bots to exploit legitimate functionality at scale.

Real-world impact: E-commerce SaaS platforms have lost millions to automated coupon abuse and fake account creation via APIs that lacked bot detection. Enterprise buyers ask whether business-critical API flows include anti-automation controls like CAPTCHA, device fingerprinting, or velocity checks.

What SaaSFort checks: SaaSFort identifies business-critical endpoints and verifies that anti-automation protections are in place for sensitive flows like registration, password reset, and payment.

API7 - Server Side Request Forgery

APIs that fetch remote resources — such as webhook URLs, image uploads, or PDF generators — can be tricked into accessing internal services. SSRF was elevated to a standalone API risk in the 2023 update due to increasing cloud adoption, where internal metadata endpoints (169.254.169.254) become high-value targets.

Real-world impact: The 2019 Capital One breach, which exposed 100 million records, was triggered by an SSRF vulnerability. Cloud-native SaaS applications face elevated SSRF risk because internal cloud metadata services can reveal credentials and configuration data. Enterprise buyers verify that URL inputs are validated against allowlists and that internal network access is blocked.

What SaaSFort checks: SaaSFort tests URL-accepting endpoints for SSRF by verifying internal IP blocking and URL validation behavior.

API8 - Security Misconfiguration

Missing security headers, verbose error messages, unnecessary HTTP methods, and permissive CORS policies fall under this category. Security misconfiguration is the most detectable API risk through automated scanning, yet it remains widespread because default configurations are often insecure.

Real-world impact: SaaSFort’s analysis shows that 45% of SaaS APIs have at least one misconfiguration — the most common being overly permissive CORS headers that allow any origin to make authenticated requests. Enterprise buyers specifically check for CORS configuration, error handling (no stack traces in production), and HTTPS enforcement.

What SaaSFort checks: SaaSFort runs over 60 configuration checks covering CORS, security headers, TLS configuration, error handling, and HTTP method enforcement. For a deep dive into continuous security monitoring, see our dedicated guide.

API9 - Improper Inventory Management

Exposed debug endpoints, old API versions still running in production, and undocumented endpoints create a shadow API surface that attackers exploit. The OWASP API Security report emphasizes that you cannot secure what you do not know exists.

Real-world impact: A 2023 study found that the average enterprise has 30% more API endpoints in production than documented. Legacy API versions with known vulnerabilities are a frequent entry point for attackers. Enterprise procurement teams ask: “Do you maintain a current API inventory?” and “What is your API versioning and deprecation policy?”

What SaaSFort checks: SaaSFort discovers API endpoints through multiple methods (documentation, JavaScript analysis, common path enumeration) and flags undocumented or deprecated endpoints that may be running without oversight.

API10 - Unsafe Consumption of APIs

When your application consumes third-party APIs without validating their responses, you inherit the security posture of every service you integrate with. This includes trusting data from webhooks, payment processors, or identity providers without sanitization.

Real-world impact: Supply chain attacks through API integrations increased 300% between 2021 and 2023. A compromised third-party API can inject malicious data into your application if responses are trusted without validation. Enterprise buyers evaluating your supply chain security will ask about third-party API validation practices.

What SaaSFort checks: SaaSFort evaluates third-party API consumption patterns, checking for input validation on external data sources and proper error handling for upstream failures.

OWASP API Security Top 10 vs OWASP Web Top 10

Understanding how the two lists overlap and differ helps SaaS CTOs prioritize remediation. The API list focuses on authorization and data exposure risks specific to programmatic access, while the web list emphasizes injection and rendering-layer attacks.

OWASP API Security Top 10	OWASP Web Top 10	Overlap
API1 - Broken Object Level Authorization	A01 - Broken Access Control	Partial — API version is more granular
API2 - Broken Authentication	A07 - Identification & Authentication Failures	High — same root cause, different attack surface
API3 - Broken Object Property Level Auth	A01 - Broken Access Control	Partial — API focuses on data filtering
API4 - Unrestricted Resource Consumption	No direct equivalent	API-specific risk
API5 - Broken Function Level Authorization	A01 - Broken Access Control	Partial — role-based access at API layer
API6 - Unrestricted Access to Business Flows	No direct equivalent	API-specific risk
API7 - Server Side Request Forgery	A10 - Server Side Request Forgery	High — same vulnerability class
API8 - Security Misconfiguration	A05 - Security Misconfiguration	High — API-specific misconfigs differ
API9 - Improper Inventory Management	No direct equivalent	API-specific risk
API10 - Unsafe Consumption of APIs	A08 - Software and Data Integrity Failures	Low — different attack vectors

Three categories — Unrestricted Resource Consumption, Unrestricted Access to Business Flows, and Improper Inventory Management — have no direct equivalent in the web Top 10. These represent purely API-specific risks that traditional web security testing does not cover. For a full breakdown of the web list, see our OWASP Top 10 for SaaS guide.

How Enterprise Buyers Test API Security

Enterprise security teams do not just read your documentation. They actively probe your APIs during vendor assessments. Here are the specific DDQ questions SaaSFort’s analysis shows appearing most frequently in enterprise procurement:

Authorization and access control:

• “Describe how your API enforces object-level authorization. Provide evidence of per-tenant data isolation.”
• “How do you prevent horizontal privilege escalation across API endpoints?”
• “What role-based access control model does your API implement?”

Authentication and session management:

• “Which authentication protocols do your APIs support (OAuth 2.0, OIDC, API keys)?”
• “What are your token expiration and rotation policies?”
• “How do you handle API key compromise and revocation?”

Rate limiting and availability:

• “What rate limiting is enforced on your API endpoints? Provide configuration evidence.”
• “How do you protect against API-layer denial of service?”

Security testing and monitoring:

• “Do you perform regular API-specific security testing (DAST, SAST, manual pen testing)?”
• “How do you maintain an inventory of all production API endpoints?”
• “What continuous monitoring do you have for API security posture changes?”

Having ready answers with supporting evidence for each of these questions accelerates the deal cycle. Vendors who prepare an enterprise security evidence package covering API security close enterprise deals 3x faster than those who scramble to gather evidence during procurement.

How SaaSFort Helps

SaaSFort scans your APIs against the OWASP API Security Top 10 and generates reports that enterprise procurement teams understand. The scanner covers 60+ security checks mapped directly to both the API Security Top 10 and OWASP ASVS Level 1 requirements.

According to SaaSFort, the most effective approach combines automated scanning with structured evidence generation. Rather than running a one-time penetration test, continuous monitoring catches regressions as your API surface evolves. Each scan produces exportable evidence that maps findings to specific OWASP categories — ready to attach to DDQ responses or share in a security evidence package.

Read the complete methodology in our SaaS Security Playbook 2026 — including the OWASP API Security Top 10 evidence templates enterprise procurement teams expect.

Frequently Asked Questions

What is the difference between OWASP Top 10 and OWASP API Security Top 10?

The OWASP Top 10 covers the most critical web application security risks (XSS, injection, broken access control), while the API Security Top 10 focuses specifically on API-layer vulnerabilities like broken object-level authorization, unrestricted resource consumption, and unsafe API consumption. Many SaaS applications need to address both lists because they have both a web frontend and an API backend serving different attack surfaces.

How do enterprise buyers evaluate API security during vendor assessments?

Enterprise procurement teams typically ask for API-specific scan results, documentation of authentication and authorization controls, rate limiting evidence, and input validation practices. These questions often appear in dedicated API sections of security questionnaires and DDQs. Buyers increasingly request continuous monitoring evidence rather than point-in-time test results.

Can automated scanning cover all OWASP API Security Top 10 risks?

Automated DAST scanners can detect many API vulnerabilities including injection flaws, security misconfigurations, and missing authentication. Business logic issues (API5, API6) and complex authorization flaws (API1, API3) often require manual review or specialized testing approaches. SaaSFort’s approach combines automated detection with guided manual verification for logic-dependent risks.

What is the most common API vulnerability in SaaS applications?

Broken Object Level Authorization (API1) is consistently the most prevalent API vulnerability. It occurs when API endpoints do not properly verify that the authenticated user is authorized to access the specific object they are requesting. According to SaaSFort’s scan data, BOLA accounts for more findings than any other single API risk category across the SaaS applications we test.

How does API security relate to OWASP ASVS compliance?

The OWASP ASVS framework includes a dedicated section (V13 - API and Web Services) that defines verification requirements for API security. ASVS Level 1 requires documented API endpoints and input validation on all API calls, making it a natural complement to API Security Top 10 testing. Vendors pursuing ASVS compliance should use API Security Top 10 testing as one input to their V13 evidence package.

How often should SaaS vendors test their APIs for OWASP compliance?

Point-in-time testing misses regressions introduced by new deployments. SaaSFort recommends running API security scans after every significant deployment and maintaining a baseline continuous monitoring schedule. Enterprise buyers prefer vendors who can show a history of clean scans over time rather than a single recent report.

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