OWASP Top 10 API Security Risks: Defending Microservices

1. Broken Object Level Authorization (BOLA)

Broken Object Level Authorization (BOLA, formerly IDOR) remains the single most common and destructive API security vulnerability. BOLA occurs when an API endpoint exposes database identifiers directly in the request path and fails to validate whether the authenticated user possesses rights to access that specific object.

For example, an authenticated user requests their account profile via `/api/v1/user/882`. If they simply modify the ID parameter to `/api/v1/user/883` and the API server returns the data of user 883 without validation, a critical authorization breach has occurred. Resolving BOLA requires enforcing access control mapping directly inside data query filters.

# Threat Vector: Attack script modifying API parameters to scrape user profiles
import requests
for user_id in range(1000, 1050):
    res = requests.get(f"https://api.site.com/v1/profile/{user_id}", headers={"Authorization": "Bearer TOKEN"})
    print(res.json())

2. Broken User Authentication & JWT Misconfiguration

JSON Web Tokens (JWT) are widely utilized in stateless microservice APIs. Misconfiguring JWT verification algorithms exposes services to massive authentication bypass attacks. A classic exploit involves setting the signature verification parameter `alg` to `"none"`.

If the API server is unhardened, it accepts unsigned tokens, allowing an attacker to modify their user ID to administrative accounts and gain full access. Securing JWTs requires enforcing explicit signature verification and storing signing keys in secure key vaults.

3. Mass Assignment Vulnerabilities

Mass Assignment occurs when API endpoints bind incoming JSON data parameters directly into database model structures without filtering. If a developer sets an update user route to process the entire incoming JSON request body, an attacker can append unexpected parameters like `"is_admin": true` or `"role": "admin"`.

To mitigate this, developers should use explicit Data Transfer Objects (DTOs) and select only designated parameters for database updates, completely blocking unauthorized field modifications.