Stack Overflow in Adonisjs with Basic Auth

When AdonisJS applications use HTTP Basic Authentication without additional protections, they can be exposed to authentication bypass via stack overflow techniques. In this context, "stack overflow" refers not only to memory-related issues but also to parser-level behaviors where malformed or deeply nested authorization headers cause frameworks to mishandle credentials. AdonisJS relies on underlying Node.js HTTP parsers, and certain malformed Basic Auth header values can trigger edge cases where authentication state is not correctly enforced.

Basic Auth encodes credentials as base64(username:password) in the Authorization header. If an attacker sends an extremely long or malformed header, some parser implementations may fail in a way that results in an empty or default credential state being accepted. In AdonisJS, when the auth pipeline does not strictly validate the format and length of the incoming header before decoding, it may inadvertently treat a malformed header as an unauthenticated request. This can lead to unauthenticated access to routes that should be protected, effectively bypassing intended access controls.

Additionally, improper route handling in AdonisJS can compound the issue. For example, if middleware responsible for Basic Auth is not consistently applied across all routes, or if route grouping logic fails to propagate authentication context, an attacker may exploit routes that appear protected but are not. The framework’s session and request lifecycle must correctly associate the authenticated user with each request; failures here can cause the application to treat authenticated and unauthenticated states inconsistently, especially under malformed input conditions.

Consider an endpoint like GET /api/admin/users that relies on AdonisJS’s built-in auth guards. If the Basic Auth middleware is misconfigured or conditionally applied, a malformed Authorization header might skip guard checks entirely. This creates a scenario where an unauthenticated user can reach sensitive endpoints, particularly when combined with route misconfiguration. Such issues are detectable by automated scanners that test unauthenticated attack surfaces, sending malformed headers to observe whether protected routes inadvertently allow access.

These risks align with common weaknesses listed in the OWASP API Security Top 10, especially Broken Object Level Authorization (BOLA) and Security Misconfiguration. Even without leveraging advanced injection techniques, poor handling of standard authentication headers can expose APIs. Using middleBrick to scan an AdonisJS endpoint with Basic Auth enabled can surface these misconfigurations by probing with malformed headers and analyzing whether authentication is enforced as expected.

To mitigate stack overflow-related authentication bypass in AdonisJS when using Basic Auth, enforce strict header validation and consistent middleware application. Always validate the format and length of the Authorization header before decoding, and ensure that all protected routes use the same authentication guard.

Here is a secure implementation example using AdonisJS v6+ with the built-in auth module. Define a custom middleware that validates the Basic Auth header format before proceeding:

// start/kernel.ts
import { middleware } from '@adonisjs/core'

export const authMiddleware = middleware(async (ctx, next) => {
  const authHeader = ctx.request.header('authorization')
  if (!authHeader || !authHeader.startsWith('Basic ')) {
    return ctx.response.unauthorized({ message: 'Missing or invalid authorization header' })
  }

  const base64Credentials = authHeader.split(' ')[1]
  if (!base64Credentials) {
    return ctx.response.unauthorized({ message: 'Invalid authorization format' })
  }

  // Optional: enforce maximum header length to prevent parser abuse
  if (authHeader.length > 200) {
    return ctx.response.unauthorized({ message: 'Request header too large' })
  }

  try {
    const decoded = Buffer.from(base64Credentials, 'base64').toString('utf-8')
    const [username, password] = decoded.split(':')
    if (!username || !password) {
      return ctx.response.unauthorized({ message: 'Invalid credentials format' })
    }
    // Attach user to context for downstream handlers
    ctx.authUser = { username }
  } catch (error) {
    return ctx.response.unauthorized({ message: 'Failed to decode credentials' })
  }

  await next()
})

Apply this middleware consistently across all protected routes in your route definitions:

// start/routes.ts
import Route from '@ioc:Adonis/Core/Route'
import { authMiddleware } from 'App/Middleware/auth'

Route.group(() => {
  Route.get('/admin/users', 'UsersController.index').middleware([authMiddleware])
  Route.post('/admin/settings', 'SettingsController.update').middleware([authMiddleware])
}).prefix('api')

For applications using AdonisJS provider-based guards, ensure your auth.ts configuration explicitly defines guards and does not allow fallback to unauthenticated access:

// config/auth.ts
import { defineConfig } from '@adonisjs/auth'

export default defineConfig({
  guards: {
    basic: {
      driver: 'basic',
      provider: 'users',
    },
  },
  default: 'basic',
})

When using middleBrick, leverage the CLI to validate your endpoints after remediation:

# Scan your API endpoint to verify authentication enforcement
middlebrick scan https://api.yourdomain.com/api/admin/users

This approach ensures that malformed headers are rejected early, reducing the risk of authentication bypass. It also aligns with findings you might see in the middleBrick dashboard, which can highlight inconsistencies in authentication coverage across routes.