Brute Force Attack in Strapi

Strapi, as a headless CMS, provides a built-in authentication system via its @strapi/plugin-users-permissions plugin. This plugin exposes REST and GraphQL endpoints for user management, including login (/api/auth/local), registration, and password reset. A brute force attack in Strapi specifically targets these authentication endpoints to guess valid credentials.

The most common attack pattern is credential stuffing or password spraying against the local login endpoint. An attacker automates requests with common passwords or breached credential pairs. Strapi's default configuration, especially in development or misconfigured production setups, may lack sufficient rate limiting on these endpoints. The attack exploits the fact that Strapi returns distinct error messages for invalid credentials vs. non-existent users, allowing user enumeration. For example, a 401 Unauthorized with { "message": "Invalid credentials" } indicates a valid username but wrong password, while 404 Not Found or a different message might indicate the user doesn't exist.

Another Strapi-specific vector is targeting the password reset token endpoint (/api/auth/forgot-password) to enumerate users or the reset confirmation endpoint (/api/auth/reset-password) to force password changes if tokens are predictable or not rate-limited. If Strapi's email service is misconfigured, an attacker might also abuse the /api/auth/email-confirmation endpoint for spam or enumeration.

Strapi's JWT-based authentication means that once credentials are guessed, the attacker obtains a token with the user's permissions. If an admin account is compromised via brute force, the attacker gains full control over content, media, and sensitive configuration data stored in Strapi's database.

Detecting brute force vulnerabilities in a Strapi API involves testing the authentication endpoints for inadequate rate limiting and user enumeration. Manually, you can use tools like curl or Burp Suite Intruder to send rapid, repeated login attempts with a known username and varying passwords, observing if responses slow down or if IP-based blocking occurs.

Using middleBrick for Detection: middleBrick's black-box scanner includes a specific Rate Limiting check that tests Strapi's authentication endpoints. When you submit a Strapi API URL (e.g., https://your-strapi.com), middleBrick automatically identifies the default auth routes (/api/auth/local, /api/auth/forgot-password) and sends sequential requests to probe for rate limit headers (X-RateLimit-Limit, Retry-After) or status code changes (e.g., 429 Too Many Requests). It also checks for user enumeration by comparing responses for valid vs. invalid usernames. The scanner reports a finding if it can make more than a threshold number of requests (e.g., 20) within a short time without being blocked or if error messages differ noticeably.

Example CLI usage to scan a Strapi instance:

middlebrick scan https://cms.example.com

The resulting report will include a Rate Limiting category score and specific findings like "Authentication endpoint lacks rate limiting" or "User enumeration possible via distinct error messages." These map directly to OWASP API Top 10: API2:2023 — Broken Authentication and API4:2023 — Unrestricted Resource Consumption.

For continuous monitoring in a CI/CD pipeline, the middleBrick GitHub Action can be configured to scan a staging Strapi API on every pull request, failing the build if the rate limiting score drops below a set threshold (e.g., B).

Remediating brute force vulnerabilities in Strapi involves configuring rate limiting at the application or proxy level and normalizing authentication error responses. Strapi v4 provides middleware for rate limiting via the @strapi/middleware/ratelimit package. Here is how to implement it:

1. Install and Configure Rate Limiting Middleware

First, install the middleware:

npm install @strapi/middleware-ratelimit

Then, configure it in config/middlewares.js to target the authentication routes specifically:

module.exports = [
  // ... other middlewares
  {
    name: 'strapi::errors',
    config: {}
  },
  {
    name: 'strapi::security',
    config: {}
  },
  {
    // Apply rate limiting only to auth endpoints
    name: 'global::ratelimit',
    config: {
      name: 'api-rate-limit',
      global: false,
      // Apply only to routes under /api/auth
      path: /^\/api\/auth\//,
      // 10 requests per minute per IP
      interval: 60000,
      max: 10,
      // Standard response on limit exceeded
      statusCode: 429,
      headers: true,
      // Use Redis for distributed rate limiting in production
      // store: require('rate-limit-redis'),
      // storeOptions: { host: 'localhost', port: 6379 }
    }
  },
  {
    name: 'strapi::logger',
    config: {}
  },
  {
    name: 'strapi::query',
    config: {}
  },
  {
    name: 'strapi::body',
    config: {}
  },
  {
    name: 'strapi::session',
    config: {}
  },
  {
    name: 'strapi::router',
    config: {}
  },
];

2. Normalize Error Messages to Prevent User Enumeration

Modify the Users Permissions plugin controller to return a generic message. Create a file src/api/user/controllers/user.js (or extend the existing controller) to override the auth callback:

'use strict';

const { createCoreController } = require('@strapi/strapi').factories;

module.exports = createCoreController('api::user.user', ({ strapi }) => ({
  async auth(ctx) {
    try {
      // Let the default logic run
      const response = await strapi.plugin('users-permissions').controllers.user.auth(ctx);
      return response;
    } catch (err) {
      // Always return the same message for any auth failure
      ctx.throw(401, 'Invalid credentials');
    }
  }
}));

This ensures that whether the username exists or not, the response is { "message": "Invalid credentials" } with a 401 status, eliminating enumeration.

3. Enable Strong Password Policies

In config/plugins.js, configure the users-permissions plugin to enforce password complexity:

module.exports = {
  'users-permissions': {
    config: {
      jwt: {
        expiresIn: '1h',
      },
      passwordPolicy: {
        minLength: 12,
        maxLength: 128,
        requireLowercase: true,
        requireUppercase: true,
        requireNumbers: true,
        requireSymbols: true,
      },
    },
  },
};

4. Use Environment-Based Rate Limiting in Production

For production, use a distributed store like Redis for rate limiting to be effective across multiple server instances. Configure the store and storeOptions in the middleware as shown in the first code example. Also, place a reverse proxy (Nginx, Cloudflare) in front of Strapi with its own rate limiting rules as a defense-in-depth measure.