Hydroadmin - HackTheBox Challenge

Description

"With reservoirs sealed and cities teetering on thirst, our heroes storm the HydroAdmin control room to reopen valves and restore the flow of water."

Target: 83.136.249.164:45091

Analysis

Initial Reconnaissance

Discovered an online code editor called "HTB Editor" at the target with the following API endpoints:

• /api/directory - list files
• /api/file?path=X - read file content
• /api/create-file - create new file
• /api/rename - rename files
• /api/restart - restart the server
• /api/verify - verify if vulnerability is patched

Source Code Analysis

Key files discovered:

index.js - Main server with Apollo GraphQL server configured with vulnerable batching:

const server = new ApolloServer({
  ...armor.protect(),
  introspection: false,
  typeDefs,
  allowBatchedHttpRequests: true,  // VULNERABLE!
  resolvers
});

models/ControlPin.js - PIN generation (4-digit, 1000-9999) and verification logic

schema/resolvers.js - GraphQL resolvers including PIN verification

exploit/solver.py - A script showing how to exploit GraphQL batching to brute-force PINs

The Vulnerability

The GraphQL server had allowBatchedHttpRequests: true which allows:

• Sending multiple GraphQL queries in a single HTTP request
• Bypassing rate limiting (10 requests per minute)
• Brute-forcing all 9000 possible PINs (1000-9999) in just a few batch requests

The Twist

This challenge required PATCHING the vulnerability, not exploiting it! The /api/verify endpoint checked if the vulnerability was fixed.

Solution

Exploitation Steps

1. Rename original file: Backup the vulnerable index.js
2. Read backup: Get the original content
3. Patch content: Change allowBatchedHttpRequests: true to allowBatchedHttpRequests: false
4. Create patched file: Write the fixed version
5. Restart server: Apply changes
6. Get flag: Verify the patch

Exploit Script

#!/usr/bin/env python3
"""
Hydroadmin - GraphQL Batching Patch Challenge
HackTheBox Challenge
"""
import requests

BASE_URL = "http://83.136.249.164:45091"

# Step 1: Rename original file to backup
print("[*] Renaming index.js to index.js.bak...")
resp = requests.post(f"{BASE_URL}/api/rename", json={
    "oldPath": "index.js",
    "newPath": "index.js.bak"
})
print(f"    Response: {resp.json()}")

# Step 2: Read the backup file
print("[*] Reading index.js.bak...")
resp = requests.get(f"{BASE_URL}/api/file?path=index.js.bak")
content = resp.json()['content']
print(f"    Got {len(content)} bytes")

# Step 3: Patch the vulnerability
print("[*] Patching allowBatchedHttpRequests...")
patched = content.replace(
    'allowBatchedHttpRequests: true',
    'allowBatchedHttpRequests: false'
)

# Step 4: Create patched file
print("[*] Creating patched index.js...")
resp = requests.post(f"{BASE_URL}/api/create-file", json={
    "path": "index.js",
    "content": patched
})
print(f"    Response: {resp.json()}")

# Step 5: Restart server
print("[*] Restarting server...")
resp = requests.post(f"{BASE_URL}/api/restart")
print(f"    Response: {resp.json()}")

# Step 6: Wait and verify
import time
print("[*] Waiting for server restart...")
time.sleep(2)

print("[*] Verifying patch...")
resp = requests.get(f"{BASE_URL}/api/verify")
result = resp.json()
print(f"    Result: {result}")

if 'flag' in result:
    print(f"\n[+] FLAG: {result['flag']}")

Vulnerable vs Fixed Code

Vulnerable (original):

const server = new ApolloServer({
  ...armor.protect(),
  introspection: false,
  typeDefs,
  allowBatchedHttpRequests: true,  // VULNERABLE
  resolvers
});

Fixed (patched):

const server = new ApolloServer({
  ...armor.protect(),
  introspection: false,
  typeDefs,
  allowBatchedHttpRequests: false,  // FIXED
  resolvers
});

Key Indicators

Use this technique when you see:

• Apollo GraphQL server with allowBatchedHttpRequests: true
• Rate limiting on GraphQL endpoint
• PIN/OTP/code verification via GraphQL
• Need to brute-force a small keyspace (e.g., 4-digit PIN)
• Online code editor with file manipulation APIs

Lessons Learned

1. GraphQL Batching Bypass: GraphQL batching can bypass rate limiting - always set allowBatchedHttpRequests: false in production Apollo servers

2. Defense in Depth: Even with @escape.tech/graphql-armor library, batching was still enabled manually - security libraries don't protect against misconfigurations

3. Patch Challenges: Sometimes CTF challenges require fixing vulnerabilities, not just exploiting them - read the challenge description carefully

4. Code Editor Attack Surface: Online code editors with file manipulation APIs (create, rename, restart) can be powerful attack vectors

5. PIN Bruteforce Math:

   • 4-digit PIN (1000-9999) = 9000 possibilities
   • Rate limit: 10 requests/minute
   • Without batching: 900 minutes = 15 hours
   • With batching (1000 queries/request): 9 requests = instant

References

• Apollo Server Batching
• GraphQL Armor
• GraphQL Security Best Practices