6 Steps to Fix Your API Security Blindspot
Written By: AKATI Sekurity Insights Team | Cybersecurity Consulting & MSSP Experts
Reading Time: 8 minutes
Key Takeaway: Application Programming Interfaces (APIs) have become the backbone of digital transformation, enabling mobile apps, cloud integrations, and partner ecosystems. Yet API security consistently ranks among the most exploited attack vectors according to OWASP's API Security Top 10 project. Organizations racing to deploy API-first architectures often expose sensitive data and business logic without the security controls applied to traditional web applications. This guide provides the six-step framework to secure your API ecosystem before attackers exploit the gaps.
The API Explosion: Why Your Attack Surface Just Multiplied
Every modern application depends on APIs. Your mobile banking app makes dozens of API calls per transaction. Your e-commerce platform connects to payment processors, inventory systems, and shipping providers through APIs. Your SaaS tools integrate via APIs. This architectural shift enables agility and innovation—but creates massive security blind spots.
The fundamental problem:
Organizations apply decades of web application security knowledge to their customer-facing websites while treating APIs as internal infrastructure requiring less scrutiny. This assumption proves catastrophically wrong. APIs expose the same sensitive data and business logic as web applications, often with direct database access and elevated privileges. Attackers understand this asymmetry and increasingly target APIs rather than hardened web frontends. The OWASP API Security Project, which tracks the most critical API security risks, documents how broken authentication, excessive data exposure, and lack of rate limiting enable attackers to bypass traditional security controls entirely. Unlike web applications where users interact through browsers with built-in security features, APIs respond to programmatic requests that can be automated, scaled, and optimized for exploitation. A vulnerability that might affect one user on a website can compromise millions of records through API abuse.
Step 1: Discover and Inventory Every API Endpoint in Your Environment
Definition: API discovery means identifying every API endpoint across your organization—including documented production APIs, undocumented shadow APIs created by development teams, legacy APIs that should be retired, zombie APIs deployed but forgotten, and third-party APIs your applications call.
Why this matters: You cannot secure what you don't know exists. Many organizations discover during security assessments that they have three to five times more API endpoints than their official API catalog documents. Development teams create APIs for specific features, contractors build integrations, acquired companies bring API portfolios, and microservices architectures generate hundreds of internal APIs. Each undocumented endpoint represents potential attack surface.
Implementation approach: Deploy API discovery tools that analyze network traffic to identify API calls, examine application code repositories to find API implementations, review API gateway logs to catalog endpoints receiving requests, and interview development teams to document shadow IT APIs. Catalog each API with critical metadata: endpoint URL, authentication requirements, data types handled (PII, financial data, health information), access privileges required, intended consumers (internal only, partner access, public), and data classification levels.
For ASEAN financial institutions: Bank Negara Malaysia's RMiT policy requires comprehensive IT asset inventories including APIs.
For US healthcare organizations: HIPAA compliance demands knowing which APIs handle Protected Health Information (PHI). Create a living API inventory updated automatically through CI/CD pipeline integration—manual catalogs become outdated the day they're completed.
Step 2: Implement Authentication and Authorization for Every API Call
Definition: API authentication verifies the identity of the caller (who are you?), while authorization validates what that caller can access (what are you allowed to do?). Every API request must pass both checks.
Common failures: The OWASP API Security Top 10 lists "Broken Object Level Authorization" as the number one API security risk. This occurs when APIs authenticate users but fail to verify they should access the specific resources requested. Example: An e-commerce API authenticates a customer, then allows that customer to view any order by changing the order ID in the request—accessing other customers' orders without additional authorization checks. Similarly, "Broken Authentication" ranks as a critical risk when APIs accept weak credentials, fail to implement rate limiting on authentication attempts, expose authentication tokens in URLs where they're logged, or don't expire tokens allowing indefinite access.
Implementation requirements: Deploy OAuth 2.0 or OpenID Connect for API authentication rather than basic authentication or API keys alone. Implement proper authorization checks at the object level—verify the authenticated user owns or has permission to access the specific resource requested, not just that they're authenticated. Use short-lived access tokens with refresh token rotation. Implement mutual TLS (mTLS) for service-to-service API authentication. Apply the principle of least privilege—APIs should receive only the minimum permissions required for their function.
Critical for regulated industries: PCI DSS Requirement 6.5.10 explicitly addresses API authentication. PDPA and GDPR require demonstrating authorized access to personal data.
Step 3: Validate and Sanitize All Input Data at the API Layer
Definition: Input validation means verifying that data sent to your API conforms to expected formats, types, ranges, and patterns before processing. Sanitization means removing or escaping potentially dangerous content.
Why APIs are vulnerable: Traditional web applications validate input through browser forms with client-side validation and Web Application Firewalls (WAFs) protecting the perimeter. APIs receive programmatic requests that bypass these controls entirely. Attackers send malicious payloads directly to API endpoints through custom scripts.
Attack patterns APIs face: Injection attacks where SQL commands, NoSQL queries, or operating system commands are embedded in API parameters. Mass assignment vulnerabilities where attackers include unexpected parameters that modify object properties they shouldn't access. XML External Entity (XXE) attacks through APIs accepting XML input. Server-Side Request Forgery (SSRF) where APIs can be tricked into making requests to internal systems.
Implementation framework: Define strict input schemas using OpenAPI Specification (formerly Swagger) that specify exact data types, formats, and ranges for every parameter. Reject requests that don't match schemas rather than attempting to coerce data into expected formats. Implement allowlists (permitted values) rather than denylists (blocked values)—denylists always miss new attack patterns. Validate data types, lengths, formats, and ranges. For string inputs, validate against expected patterns using regular expressions. Sanitize any output that might be rendered in client applications. Deploy API security gateways that enforce validation policies before requests reach application code.
For PCI DSS compliance: Requirement 6.5.1 specifically mandates protection against injection flaws in all applications including APIs.
Step 4: Implement Rate Limiting and Resource Quotas to Prevent Abuse
Definition: Rate limiting restricts how many API requests a client can make within a specified time period, while resource quotas limit consumption of computational resources like data retrieved, records modified, or processing time consumed.
The business logic attack vector: Unlike infrastructure attacks that try to crash systems, business logic attacks use legitimate API functionality in ways that harm the business. Attackers automate credential stuffing attempts through authentication APIs, scrape entire product catalogs through inventory APIs, test stolen credit cards through payment APIs, or query customer databases to exfiltrate PII. These attacks use valid API calls that appear legitimate individually but become malicious at scale.
Real-world impact: Attackers automate account enumeration through password reset APIs to identify valid usernames. They use price-check APIs to monitor competitor pricing in real-time. They exploit unlimited API queries to extract entire databases record-by-record. Without rate limiting, a single compromised API key can query millions of records before detection.
Implementation strategy: Implement rate limiting at multiple levels: per user/API key (100 requests per minute), per endpoint (authentication endpoints get stricter limits than public read-only endpoints), per IP address (to catch attackers using multiple accounts), and per organization for B2B APIs. Set resource quotas limiting records returned per request, total data retrieved per day, or processing time per request. Implement exponential backoff—temporary rate limit violations trigger warnings, repeated violations trigger longer lockouts. Monitor rate limit violations for patterns indicating attacks versus legitimate traffic spikes. Return meaningful HTTP 429 (Too Many Requests) responses with retry-after headers.
Important distinction: Rate limiting differs from DDoS protection. Rate limiting prevents abuse of business logic; DDoS protection prevents infrastructure overload. You need both.
Step 5: Encrypt API Traffic and Protect Sensitive Data in Transit and at Rest
Definition: API security requires encrypting all communication channels using TLS 1.3 (or minimum TLS 1.2), protecting sensitive data stored in databases and logs, and minimizing data exposure in API responses.
The data exposure problem: OWASP identifies "Excessive Data Exposure" as a top API security risk. APIs often return complete database objects to clients, relying on client applications to filter sensitive fields before display. Attackers bypass client apps and call APIs directly, receiving unfiltered responses containing social security numbers, passwords, account balances, or other sensitive data the UI would hide. Example: A mobile app displays user profiles showing name and photo. The underlying API returns the complete user object including email, phone number, address, and date of birth. Attackers call the API directly to harvest PII for all users.
Implementation requirements: Enforce TLS 1.3 for all API communications—reject unencrypted HTTP requests. Implement certificate pinning for mobile and desktop applications to prevent man-in-the-middle attacks. Design API responses to return only data the client needs—implement field filtering so clients specify which attributes they require. Never include sensitive data like passwords or full credit card numbers in API responses. Redact sensitive fields in logs—API gateway logs should mask authentication tokens, PII, and financial data. Encrypt sensitive data at rest in databases with proper key management. For APIs handling payment card data, implement point-to-point encryption meeting PCI DSS requirements. For healthcare APIs handling PHI, ensure encryption satisfies HIPAA Security Rule requirements.
Critical for cross-border data: PDPA, GDPR, and data localization laws require knowing where API-transmitted data resides and transits.
Step 6: Monitor API Traffic for Anomalies and Security Events
Definition: API security monitoring means analyzing API request patterns, authentication attempts, data access behaviors, and error responses to detect attacks, abuse, and policy violations in real-time.
What to monitor: Track authentication failures by user, endpoint, and IP address to identify credential stuffing or brute force attacks. Monitor rate limit violations that indicate scraping or automated abuse. Analyze data access patterns to detect unusual queries like sequential ID enumeration or bulk data extraction. Track error rates by endpoint and user—spikes in 400-series errors indicate input validation attacks or reconnaissance. Monitor geographic anomalies where API access originates from unexpected countries. Analyze time-based patterns to detect activity during unusual hours. Track API version usage to identify calls to deprecated endpoints that should no longer receive traffic.
Implementation architecture: Integrate API gateways with Security Information and Event Management (SIEM) platforms. Configure APIs to generate structured logs including timestamp, authenticated user, source IP, endpoint accessed, HTTP method, parameters submitted, response code, and response time. Implement User and Entity Behavior Analytics (UEBA) to establish baseline API usage patterns per user and application, then alert on deviations. Deploy API threat detection tools that identify OWASP API Top 10 attack patterns in traffic. Create runbooks for common API security events: account credential stuffing, data exfiltration attempts, API key compromise, and privilege escalation attempts.
Measurable outcomes: Establish Mean-Time-To-Detect (MTTD) and Mean-Time-To-Respond (MTTR) metrics specifically for API security incidents. Set targets for detecting API attacks within minutes rather than days.
AKATI Sekurity: Securing Your API-First Architecture Across ASEAN and Beyond
Modern applications depend on APIs, but most organizations lack the specialized expertise to secure them effectively. Traditional web application security approaches miss API-specific vulnerabilities documented in the OWASP API Security Top 10.
AKATI Sekurity's API Security Services:
Our Penetration Testing team specializes in API security assessments, testing authentication and authorization controls, input validation, rate limiting effectiveness, and data exposure vulnerabilities using the OWASP API Security Testing methodology. We discover undocumented and shadow APIs through comprehensive attack surface mapping.
Our Cybersecurity Consulting services design API security architectures including API gateway selection and configuration, authentication and authorization frameworks (OAuth 2.0, OpenID Connect), and API security policies aligned with your regulatory requirements (PCI DSS, PDPA, HIPAA, GDPR). We help development teams implement secure API design patterns and integrate security into CI/CD pipelines.
Through 24/7 Managed Security Services (MSSP), we monitor API traffic in real-time, detecting credential stuffing attacks, data exfiltration attempts, and business logic abuse before they impact your business. Our Security Operations Center analysts understand API-specific attack patterns that traditional network monitoring misses.
Our Security Posture Assessments include API inventory and risk evaluation, identifying which APIs handle sensitive data, lack proper authentication, or expose excessive information.
Geographic expertise: With operations across ASEAN and partnerships in North America, we understand both US compliance frameworks (PCI DSS, HIPAA, SOC 2) and regional requirements (BNM RMiT, MAS TRM, PDPA).
Ready to secure your API ecosystem before attackers exploit the gaps? Contact AKATI Sekurity at hello@akati.com.
About the Author: This article was developed by AKATI Sekurity's cybersecurity consulting and penetration testing teams with expertise in API security across financial services, healthcare, e-commerce, and technology sectors in ASEAN and North America.
Related Services: Penetration Testing | Cybersecurity Consulting | 24/7 Managed Security (MSSP) | Security Posture Assessment
References:
OWASP API Security Project: https://owasp.org/www-project-api-security/
OWASP API Security Top 10 2023: https://owasp.org/API-Security/editions/2023/en/0x11-t10/
