Buffer Overflow in Hapi with Basic Auth

A buffer overflow in a Hapi server using Basic Authentication can arise when user-controlled credentials are processed without length constraints and the application copies credential data into fixed-size buffers. In a black-box scan, middleBrick tests unauthenticated attack surfaces and checks categories such as Input Validation and BFLA/Privilege Escalation, which can surface risky handling of authentication headers.

With Basic Auth, the client sends an Authorization header of the form Authorization: Basic base64(username:password). If the server decodes this value and copies the resulting string into a fixed-length C buffer (for example via functions like strcpy, sprintf, or unsafe C string manipulation in native add-ons), a long username or password can overflow the destination buffer. This may lead to memory corruption, arbitrary code execution, or crashes. Even in JavaScript, unsafe practices such as using Buffer.from() with user-controlled sizes or concatenating credentials into fixed-size message formats can create similar risks when the underlying native bindings are involved.

middleBrick’s LLM/AI Security checks do not test for buffer overflow directly, but the scanner’s Input Validation and Unsafe Consumption checks can flag missing length validation on authentication inputs and unsafe handling of decoded credentials. For example, if a route extracts the decoded payload and uses it to build responses or store in fixed-size structures without sanitization, the scan may surface the issue with severity and remediation guidance.

Consider a native add-on used by a Hapi server:

// Example native add-on (C) — unsafe strcpy
#include <node_api.h>
#include <string.h>

static napi_value setCredentials(napi_env env, napi_callback_info info) {
  size_t argc = 2;
  napi_value args[2];
  napi_get_cb_info(env, info, &argc, args, NULL, NULL);
  char username[64];  // Fixed-size buffer
  char password[64];
  size_t written;
  napi_get_value_string_utf8(env, args[0], username, sizeof(username), &written);
  napi_get_value_string_utf8(env, args[1], password, sizeof(password), &written);
  // If username or password exceed 63 chars + null terminator, overflow occurs
  return NULL;
}

If such an add-on is invoked with long credentials from Basic Auth, the overflow is triggered before any business logic runs. The scanner’s Inventory Management and Data Exposure checks may highlight risky storage or logging of credentials, while Property Authorization and Rate Limiting tests ensure the endpoint does not expose unbounded or mis-scoped access.

Remediation focuses on validating credential length, avoiding fixed-size buffers, using safe string handling, and leveraging built-in Hapi and Node.js facilities. Always treat Authorization header values as untrusted input.

• Validate length and format before use: enforce reasonable upper bounds for username and password (e.g., 256 characters) and reject malformed credentials early.
• Use Node.js Buffers safely: prefer Buffer.from(string) without fixed-size copies, and avoid C-style string operations in native add-ons unless necessary and properly bounded.
• Do not log or store raw credentials; use hashes or tokens for session management.
• Apply Hapi’s built-in auth schema validation to enforce constraints on payloads and headers.

Safe Hapi route example with Basic Auth parsing and validation:

const Hapi = require('@hapi/hapi');
const bcrypt = require('bcrypt');

const users = new Map(); // In practice, use a secure store
users.set('alice', await bcrypt.hash('StrongPassword123!', 10));

const validateCredentials = (username, password) => {
  if (!username || typeof username !== 'string' || username.length > 256) {
    throw new Error('Invalid username');
  }
  if (!password || typeof password !== 'string' || password.length > 256) {
    throw new Error('Invalid password');
  }
  return true;
};

const server = Hapi.server({ port: 4000, host: 'localhost' });

server.auth.scheme('custombasic', () => ({
  authenticate(request, h) {
    const header = request.headers.authorization;
    if (!header || !header.startsWith('Basic ')) {
      return h.authenticated({ credentials: null, artifacts: null }).fail({
        statusCode: 401,
        error: 'Unauthorized',
        message: 'Missing Authorization header'
      });
    }
    const decoded = Buffer.from(header.slice(6), 'base64').toString('utf8');
    const separator = decoded.indexOf(':');
    if (separator === -1) {
      return h.authenticated({ credentials: null, artifacts: null }).fail({
        statusCode: 401,
        error: 'Unauthorized',
        message: 'Malformed credentials'
      });
    }
    const username = decoded.slice(0, separator);
    const password = decoded.slice(separator + 1);
    try {
      validateCredentials(username, password);
    } catch (err) {
      return h.authenticated({ credentials: null, artifacts: null }).fail({
        statusCode: 400,
        error: 'Bad Request',
        message: err.message
      });
    }
    const expected = users.get(username);
    if (!expected) {
      return h.authenticated({ credentials: null, artifacts: null }).fail({
        statusCode: 401,
        error: 'Unauthorized',
        message: 'Invalid credentials'
      });
    }
    const isValid = bcrypt.compareSync(password, expected);
    if (!isValid) {
      return h.authenticated({ credentials: null, artifacts: null }).fail({
        statusCode: 401,
        error: 'Unauthorized',
        message: 'Invalid credentials'
      });
    }
    return h.authenticated({ credentials: { username }, artifacts: null });
  }
}));

server.auth.strategy('default', 'custombasic');
server.route({
  method: 'GET',
  path: '/secure',
  options: {
    auth: 'default',
    handler: (request, h) => {
      return { message: `Welcome, ${request.auth.credentials.username}` };
    }
  }
});

const start = async () => {
  await server.start();
  console.log('Server running on %s', server.info.uri);
};

start().catch(err => console.error(err));

If you use native add-ons, ensure they perform bounds checking (e.g., using napi_get_value_string_utf8 with size limits or strncpy with explicit truncation and null termination). Prefer higher-level APIs that avoid manual buffer management entirely. middleBrick’s CLI can scan your endpoints to verify that authentication inputs are properly validated and that no unsafe consumption patterns are exposed.