Null Pointer Dereference in Adonisjs with Basic Auth

A null pointer dereference in AdonisJS when Basic Auth is used typically occurs because the authentication layer does not guarantee that a user record exists for the provided credentials. When you configure HTTP Basic Auth, AdonisJS resolves the user by a lookup (often via a callback or model query). If the lookup returns null or undefined (for example, because the username does not exist, the account is disabled, or the query throws an unhandled exception), and application code immediately dereferences the result without a null check, Node.js throws an uncaught exception, leading to a 500 response and potential information leakage.

This combination is risky because Basic Auth sends credentials on every request; an attacker can probe usernames by observing differences in behavior (e.g., timing or error messages) when null dereferences occur for valid versus invalid users. If error handling is not uniform, stack traces or exception messages may expose internal paths or variable names, aiding further exploitation. In AdonisJS, routes or middleware that directly chain auth guards with downstream logic are vulnerable when the resolved user object is assumed to be present.

For example, consider a route that relies on an authenticated user without validating existence:

import { schema } from '@ioc:Adonis/Core/Validator'
import { HttpContextContract } from '@ioc:Adonis/Core/HttpContext'

export default class SessionsController {
  public async store({ auth, request }: HttpContextContract) {
    const { username, password } = request.only(['username', 'password'])
    // Auth guard may resolve to null if user not found
    const user = await auth.use('api').authenticate()
    // Potential null pointer dereference if user is null
    const role = user.role // TypeError: Cannot read properties of null (reading 'role')
    return { role }
  }
}

In this pattern, if the authentication guard cannot find a matching user, user can be null, and accessing user.role causes a null pointer dereference. This is especially problematic when Basic Auth callbacks do not handle missing users gracefully, and the framework’s default error handling surfaces the raw exception to the client.

Additionally, if you use a custom Basic Auth callback that queries the database and the query throws or returns null, unhandled rejections or exceptions can propagate to the HTTP layer, again resulting in a 500 status that reveals stack traces. The scanner checks for such error handling inconsistencies under the Authentication and Input Validation checks, noting whether the application provides uniform error responses that do not leak internal details.

Remediation focuses on ensuring the resolved user is always verified for nullity before use and that authentication failures produce safe, uniform responses. Below are concrete, safe patterns for handling Basic Auth in AdonisJS.

1) Explicit null checks after authentication

Always check the resolved user object before accessing its properties. Use optional chaining or conditional guards to avoid dereferencing null.

import { schema } from '@ioc:Adonis/Core/Validator'
import { HttpContextContract } from '@ioc:Adonis/Core/HttpContext'

export default class SessionsController {
  public async store({ auth, response }: HttpContextContract) {
    const user = await auth.use('api').authenticate()
    if (!user) {
      return response.unauthorized('Invalid credentials')
    }
    // Safe: user is guaranteed non-null here
    const role = user.role
    return { role }
  }
}

2) Use a verified user assertion helper

Create a small utility to centralize authentication and null handling, ensuring consistent behavior across routes.

// utils/ensureAuthenticated.ts
import { HttpContextContract } from '@ioc:Adonis/Core/HttpContext'

export function ensureAuthenticated(ctx: HttpContextContract) {
  const user = ctx.auth.getUser()
  if (!user) {
    ctx.response.unauthorized('Authentication required')
    return null
  }
  return user
}

// In a route handler
import { ensureAuthenticated } from 'App/Helpers/ensureAuthenticated'

export default class ProfileController {
  public show({ response }: HttpContextContract) {
    const user = ensureAuthenticated(response)
    if (!user) {
      return // response already sent
    }
    return { id: user.id, email: user.email }
  }
}

3) Configure auth guards with proper user resolution and fallback

Define your auth provider to return a clear result and avoid throwing on missing users. In start/auth.ts, customize the callback to handle missing users explicitly:

import { BaseUserProvider } from '@ioc:Adonis/Addons/Auth'
import User from 'App/Models/User'

const authProvider: BaseUserProvider = {
  async getUser(uid) {
    try {
      return await User.find(uid)
    } catch {
      return null
    }
  },
}

export default authProvider

4) Validate input before authentication

Ensure incoming identifiers conform to expectations before attempting auth resolution. This reduces unexpected nulls from malformed requests.

import { schema } from '@ioc:Adonis/Core/Validator'

const basicAuthSchema = schema.create({
  username: schema.string({ trim: true, escape: false }),
  password: schema.string(),
})

export default class AuthController {
  public async login({ request, auth, response }: HttpContextContract) {
    const payload = request.validate({ schema: basicAuthSchema })
    const user = await auth.use('api').attempt(payload.username, payload.password)
    if (!user) {
      return response.unauthorized('Invalid credentials')
    }
    return { token: user.generateJwt() }
  }
}

These patterns ensure that null pointer dereferences are prevented by design, and Basic Auth failures are handled without exposing internal errors. The middleBrick CLI can be used to verify that your endpoints no longer produce authentication-related null dereferences by scanning with the middlebrick scan <url> command and reviewing findings under Authentication and Input Validation.