Shellshock in Adonisjs with Jwt Tokens

Shellshock (CVE-2014-6271 and related variants) is a command injection vulnerability in the Bourne Again Shell (bash) that arises when function exports are followed by code in environment variable values. In AdonisJS applications that use JWT tokens for authentication, the risk emerges when token payload values or derived environment variables are passed into shell commands without proper sanitization. If your AdonisJS server decodes a JWT and then uses values from the token (e.g., username, scope, or a user-supplied identifier) to construct shell commands—either directly or via environment variables—an attacker can craft a malicious token to execute arbitrary code on the host.

Consider an example where an API endpoint reads a JWT claim and uses it to build a shell invocation, such as generating a report or calling an external CLI tool. If the claim is interpolated into the command string without validation, a token like {"sub":"admin;id"} can lead to unintended command execution. This becomes an exposure when the application runs in environments where bash processes environment variables, and the token-derived data flows into those variables. Even in black-box scanning, middleBrick tests for such injection paths by analyzing endpoint behavior and inspecting OpenAPI specs for places where external calls might occur, highlighting risky integrations between identity tokens and system commands.

Additionally, unauthenticated LLM endpoints or misconfigured serverless functions that rely on JWTs for identity can inadvertently propagate unsafe values into shell contexts. For instance, if an environment variable such as REPORT_USER is set from a JWT claim and later used by a bash script, an attacker who can influence the JWT can exploit the Shellshock vector. MiddleBrick’s checks for Input Validation and Unsafe Consumption are designed to detect these data flows and the presence of external calls that may be vulnerable, mapping findings to OWASP API Top 10 and providing remediation guidance to break the injection chain.

To mitigate Shellshock-related risks when using JWT tokens in AdonisJS, ensure that token claims are never directly interpolated into shell commands. Use structured, non-shell APIs for external operations, and strictly validate and sanitize all inputs derived from JWTs. Below are concrete code examples demonstrating secure practices.

• Avoid shell interpolation; use Node.js child process APIs with argument arrays:

import { execFile } from 'node:child_process'
import { verify } from 'jsonwebtoken'

export async function handleReport(token: string) {
  const decoded = verify(token, process.env.JWT_SECRET!) as { sub: string }
  // Safe: use execFile with arguments array, no shell interpolation
  const { stdout } = await execFile('reportgen', ['--user', decoded.sub])
  return stdout
}

• If you must use shell commands, rigorously validate and escape token-derived values:

import { escape } from 'node:querystring'
import { verify } from 'jsonwebtoken'

export function getUserInfo(token: string) {
  const decoded = verify(token, process.env.JWT_SECRET!) as { email: string }
  const safeEmail = escape(decoded.email)
  // Only if shell usage is unavoidable; prefer non-shell alternatives
  return `user-email=${safeEmail}`
}

• Set environment variables safely without relying on untrusted data from JWTs:

import { verify } from 'jsonwebtoken'

export function configureEnv(token: string) {
  const decoded = verify(token, process.env.JWT_SECRET!) as { scope: string }
  // Validate scope against an allowlist instead of using it directly
  const allowedScopes = ['read', 'write']
  if (!allowedScopes.includes(decoded.scope)) {
    throw new Error('Invalid scope')
  }
  // Do not export raw token claims into environment variables
  process.env.APP_SCOPE = decoded.scope
}

• In your OpenAPI spec, document that endpoints using JWTs do not invoke shell commands, and use middleBrick to validate this behavior. The CLI command middlebrick scan <url> can be integrated into your workflow to continuously check for risky patterns. For teams requiring deeper assurance, the Pro plan provides continuous monitoring and CI/CD integration to fail builds if insecure token handling is detected.