Web Hacking Series - Part 19: API Security – Hacking🔌🛡️🚀

rocky

Hey guys, Rocky here! 🌐🔓

Welcome to Day 19 of the Daily Web Hacking series! Today, we’re diving into API Security—the backbone of modern web apps and a goldmine for attackers. Whether it’s REST, GraphQL, or gRPC, APIs handle sensitive data, business logic, and user interactions. But misconfigured or poorly secured APIs can turn into gateways for breaches. Let’s explore how hackers exploit APIs and how to lock them down.

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Why API Security Matters

APIs power everything from mobile apps to microservices, but they’re also prime targets:

80% of web traffic flows through APIs (Cloudflare, 2023).
OWASP API Top 10 highlights critical risks like broken auth, data exposure, and misconfigurations.
Real-World Breaches: Facebook (2018), Peloton (2021), and T-Mobile (2023) all suffered API-related leaks.

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1. REST API Hacking

REST (Representational State Transfer) uses HTTP methods (GET, POST, PUT, DELETE) and is widely adopted. Common vulnerabilities include:

A. Insecure Endpoints

Example: An unprotected /api/users endpoint leaking all user data.

  GET /api/users HTTP/1.1  
  Host: example.com

→ Response:

  [{"id":1,"email":"admin@example.com","role":"admin"},...]

Exploit: Use Postman or curl to probe endpoints.

B. Broken Object-Level Authorization (BOLA/IDOR)

Example: Accessing another user’s data by tampering with IDs:

  GET /api/orders/123 HTTP/1.1  # Change to /api/orders/124

Mitigation: Implement role-based access control (RBAC) and validate user permissions.

C. Injection Attacks

SQLi:

  GET /api/products?category=Gadgets' OR 1=1-- HTTP/1.1

Command Injection:

  POST /api/export  
  { "format": "pdf; rm -rf /" }

Tools: Burp Suite, SQLmap.

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2. GraphQL API Hacking

GraphQL’s flexibility allows precise queries but introduces unique risks:

A. Introspection Attacks

Exploit: Query the schema to discover hidden fields or mutations.

  query { __schema { types { name fields { name } } } }

→ Exposes internal types like User, Admin, or deleteAccount.

Mitigation: Disable introspection in production using GraphQL Armor.

B. Query Overload (DoS)

Example: A recursive query exhausting server resources:

  query { posts { comments { replies { comments { ... } } } } }

Defense: Limit query depth, cost analysis, and rate limiting.

C. Data Exposure

Exploit: Over-fetching sensitive fields:

  query { users { email apiKey } }

Fix: Implement field-level permissions and sanitize responses.

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3. gRPC API Hacking

gRPC uses HTTP/2 and Protocol Buffers (binary format), but risks include:

A. Insecure Deserialization

Example: Malicious protobuf payloads triggering RCE:

  message Exploit {  
    optional string cmd = 1 [default = "rm -rf /"];  
  }

Mitigation: Validate protobuf schemas and use safe deserialization libraries.

B. Unauthenticated Services

Exploit: Bypassing auth in .proto service definitions:

  service UserService {  
    rpc GetUser (UserRequest) returns (User) {}  // No auth decorator  
  }

Defense: Enforce TLS and use interceptors for JWT/OAuth validation.

C. Reflection Attacks

Tool: grpcurl to enumerate services:

  grpcurl -plaintext example.com:50051 list

Fix: Disable server reflection in production.

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Top API Security Tools

Postman: Test REST endpoints and automate attacks.
GraphQLmap: Exploit GraphQL vulnerabilities (DoS, introspection).
grpcui: Inspect and manipulate gRPC services.
OWASP ZAP: Automated API scanning for REST/GraphQL.
Burp Suite: Intercept and tamper with API requests.

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OWASP API Top 10 (2023) – Quick Hits

Broken Object-Level Authorization: Always validate user access.
Broken Authentication: Secure tokens (JWT, OAuth) and avoid hard-coded keys.
Excessive Data Exposure: Never trust client-side filtering.
Lack of Resources & Rate Limiting: Prevent DoS with quotas.
Broken Function-Level Authorization: Enforce RBAC at all layers.

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Real-World Breaches

Peloton (2021): Unauthenticated API endpoints exposed user data.
T-Mobile (2023): GraphQL query overload crashed systems.
Facebook Token Leak (2018): Misconfigured OAuth exposed 50M tokens.

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Securing APIs: Best Practices

Authentication: Use OAuth 2.0, JWT with short-lived tokens.
Input Validation: Sanitize all inputs (REST params, GraphQL queries, protobufs).
Encryption: Enforce HTTPS (TLS 1.3) for data in transit.
Rate Limiting: Block abusive clients with tools like Kong or AWS WAF.
Logging & Monitoring: Detect anomalies with Elasticsearch or Datadog.

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Final Thoughts

APIs are the lifeblood of modern apps, but they’re also the weakest link if mishandled. By understanding REST, GraphQL, and gRPC vulnerabilities—and adopting rigorous testing and hardening practices—you can turn APIs from liabilities into fortresses.

Next Up: Day 20: Web Cache Poisoning – Manipulating What the World Sees

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Rocky out! ✌️

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P.S. If you’re enjoying this series, share it with your team! Let’s turn “We’ll secure it later” into “We locked it down today.”

Discussion Question: What’s the craziest API vuln you’ve found? I once discovered a gRPC service with no auth returning admin passwords. 😱 Spill your stories below! 👇