APIs are the most exposed layer of modern applications—and often the least protected.In many breaches, the same weaknesses appear repeatedly: overlooked configurations, excessive privileges, and misplaced trust in “internal” boundaries.The following five red flags represent common API flaws that attackers quickly identify and exploit.
1. Over-Permissive Tokens Description: Access tokens that grant excessive privileges across roles, scopes, or services.
Risk:
A single leaked token can expose sensitive endpoints, including administrative or internal APIs.
Tokens frequently leak through logs, SDKs, session storage, or third-party integrations.
Mitigation:
Apply least-privilege principles.
Limit scopes and reduce token lifetime (especially for JWTs).
Rotate tokens and monitor scope usage.
Enforce access control on the server side.
2. No Rate Limiting or Abuse Protection
Description: APIs that allow unlimited requests without throttling, filtering, or anomaly detection.
Risk:
Enables brute-force, credential stuffing, and account enumeration attacks.
Creates performance issues for legitimate users.
Mitigation:
Implement global and per-user rate limits.
Use CAPTCHA or step-up authentication for suspicious activity.
Apply velocity checks, IP reputation scoring, and anomaly detection.
3. No Schema Validation
Description: APIs that accept arbitrary JSON or payloads without type checking or structural enforcement.
Risk:
Attackers exploit malformed input to bypass logic or inject malicious data.
Increases likelihood of deserialization issues, injection vulnerabilities, and data corruption.
Mitigation
Validate requests against OpenAPI specifications or JSON Schema.
Reject unknown fields, invalid types, and malformed input.
Automate schema testing and maintain version control.
4. Unauthenticated Internal Endpoints
Description: “Private” APIs deployed without authentication because they are assumed to be used only by internal services.
Risk:
Internal exposure is not equivalent to security.
Misconfigured proxies, SSRF exploits, or VPN leaks can expose these endpoints to attackers.
Mitigation:
Apply zero trust principles to all services.
Protect endpoints using mTLS, API gateways, or service mesh policies.
Log internal API access with the same rigor as external traffic.
5. Wildcard Routes and No Logging
Description: Catch-all routes (/*) handling multiple operations without granular logging or access control.
Risk:
Provides ambiguity that attackers exploit by fuzzing undocumented or forgotten routes.
Lack of detailed logging prevents detection of suspicious access attempts.
Wildcard routes may act as proxies, aiding lateral movement.
Mitigation:
Avoid wildcard routes except when strictly necessary, and protect them with strong authentication.
Implement detailed request/response logging with trace identifiers.
Monitor for scanning behavior such as bursts of 404 errors or unusual route exploration.
Conclusion
These five issues are among the most common weaknesses that attackers detect almost immediately during reconnaissance. Addressing them early strengthens overall API security posture and reduces the likelihood of successful exploitation.
