Brute Force Attack in Strapi (Typescript)

A brute force attack against a Strapi API often targets the local authentication endpoint (/api/auth/local). Attackers submit many username or email combinations with varying passwords to eventually guess valid credentials. Strapi’s default behavior can unintentionally support this: if responses differ based on whether the user exists (e.g., returning 200 with a JWT for valid users versus a generic 400 error for invalid ones), an attacker can learn which accounts are valid and iterate more efficiently.

When you implement custom logic in Strapi using Typescript—for example, extending controllers or writing custom middleware—you may inadvertently introduce timing differences or verbose error messages that aid enumeration. Typescript code that leaks existence via response status codes or body content increases the attack surface. For instance, a controller that first finds a user by email and then compares state before deciding the error response can expose timing or behavioral distinctions.

Additionally, if rate limiting is not enforced at the Strapi application layer or is misconfigured in Typescript middleware, attackers can make repeated requests without meaningful throttling. Even when using Strapi’s built-in admin panel, weak account policies (e.g., no minimum password strength or no account lockout) facilitate brute force attempts. The unauthenticated attack surface matters here: public endpoints that rely on predictable identifiers (like sequential IDs) combined with weak authentication workflows are especially susceptible.

Consider a custom Typescript controller that overrides the default authentication flow. If it returns { error: 'Invalid credentials' } for bad passwords but a JWT for good ones, an attacker can distinguish success from failure. A safer approach keeps behavior consistent and defers validation to a rate-limited stage, reducing information leakage.

Remediation focuses on making authentication responses uniform and adding robust rate limiting. In Strapi, you can customize the authentication controller using Typescript to avoid leaking user existence and to enforce request throttling. Ensure that the same HTTP status code and similar response shape are returned for both invalid credentials and missing users.

Example: a custom authentication controller in src/api/auth/controllers/AuthController.ts that avoids information leakage and integrates rate limiting via a Typescript middleware.

import { factory } from '@strapi/strapi';

export default factory('plugin::users-permissions.auth').configure({
  async login(ctx) {
    const { identifier, password } = ctx.request.body;

    // Fetch user by email or username; do not reveal which one exists
    const user = await strapi.entityService.findOne('plugin::users-permissions.user', identifier, {
      populate: ['role'],
    }).catch(() => null);

    // Constant-time check simulation: always perform a dummy hash operation
    const dummyHash = await strapi.plugins['users-permissions'].services.user.hashPassword(password, { pepper: process.env.PEPPER });

    // Verify credentials only if user exists; keep response shape consistent
    if (!user || !(await strapi.plugins['users-permissions'].services.user.validatePassword(password, user))) {
      ctx.status = 400;
      return { error: 'Invalid credentials' };
    }

    // Generate JWT (Strapi internal handling)
    const jwt = strapi.plugins['users-permissions'].services.jwt.issue({ id: user.id });
    return { jwt, user: { id: user.id, username: user.username, email: user.email } };
  },
});

In this Typescript example, the controller avoids branching on user existence before hashing, and it returns a generic error message with a 400 status for both invalid credentials and non-existent identifiers. This reduces attacker ability to distinguish valid accounts.

Also enforce rate limiting at the plugin or server level. Strapi’s configuration can include a policy that limits requests per IP or per identifier. In custom Typescript middleware, you can integrate a simple in-memory or Redis-based rate limiter, but ensure it runs before the authentication logic:

import { Middleware } from '@strapi/strapi';

const rateLimit = new Map();

export default () => {
  return async (ctx, next) => {
    if (ctx.path === '/auth/local' && ctx.method === 'POST') {
      const ip = ctx.ip;
      const now = Date.now();
      const window = 60_000; // 1 minute
      const limit = 10;

      if (!rateLimit.has(ip)) {
        rateLimit.set(ip, []);
      }
      const timestamps = rateLimit.get(ip).filter(t => now - t < window);
      if (timestamps.length >= limit) {
        ctx.status = 429;
        ctx.body = { error: 'Too many requests' };
        return;
      }
      timestamps.push(now);
      rateLimit.set(ip, timestamps);
    }
    await next();
  };
};

Combine this with Strapi’s built-in security settings: enforce strong password policies, enable account lockout after repeated failures at the plugin configuration, and use the dashboard or CLI to monitor authentication logs. These Typescript-centric adjustments help ensure brute force attempts face consistent responses and are throttled effectively.