Container Escape in Strapi

Container escape vulnerabilities in Strapi typically emerge through the plugin system and file upload functionality. Strapi's extensible architecture allows developers to create custom plugins that can inadvertently introduce escape vectors.

The most common manifestation occurs in Strapi's file upload handlers. When Strapi processes uploaded files, it often uses Node.js's child_process module for tasks like image optimization or archive extraction. If these operations aren't properly sandboxed, an attacker can craft malicious inputs to break out of the container.

// Vulnerable Strapi upload handler (common pattern)
const { exec } = require('child_process');
const path = require('path');

async uploadFile(file) {
  const tempPath = path.join('/tmp', file.name);
  await file.mv(tempPath);
  
  // Dangerous: no input validation or sandboxing
  exec(`convert ${tempPath} -resize 200x200 /uploads/${file.name}`, (err, stdout, stderr) => {
    if (err) console.error(err);
  });
}

Another Strapi-specific vector is through GraphQL resolvers. Strapi's GraphQL plugin allows custom resolvers that can execute arbitrary system commands if developers aren't careful with input sanitization.

// Vulnerable Strapi GraphQL resolver
const { exec } = require('child_process');

module.exports = {
  Query: {
    systemInfo: async (_, args) => {
      // Direct command injection possible
      const command = `uname -a && whoami && ls -la ${args.path || '/tmp'}`;
      return new Promise((resolve, reject) => {
        exec(command, (err, stdout, stderr) => {
          if (err) return reject(err);
          resolve(stdout);
        });
      });
    }
  }
};

Strapi's admin panel authentication bypass can also lead to container escape. If an attacker gains admin access, they can upload malicious plugins or modify existing ones to execute code outside the container's intended boundaries.

Detecting container escape vulnerabilities in Strapi requires both static analysis and runtime scanning. middleBrick's API security scanner specifically targets Strapi's unique attack surface with these checks:

Plugin System Analysis: middleBrick examines Strapi's plugin architecture for unsafe require() calls and dynamic module loading that could be exploited for escape.

# Using middleBrick CLI to scan Strapi API
middlebrick scan https://api.strapi.example.com \
  --spec https://api.strapi.example.com/graphql \
  --output report.json

The scanner identifies risky patterns like child_process.exec() calls with unvalidated inputs, path traversal in file operations, and unsafe GraphQL resolvers.

Runtime Detection: middleBrick actively tests Strapi's upload endpoints with malicious payloads designed to trigger container escape attempts without actually breaking out. It looks for error messages that reveal system paths or command execution capabilities.

Configuration Analysis: The scanner checks Strapi's package.json, ecosystem.config.js, and Docker configurations for overly permissive settings that could facilitate escape.

middleBrick's LLM security module is particularly relevant for Strapi instances using AI features, as prompt injection could be used to exfiltrate system information that aids container escape planning.

Securing Strapi against container escape requires a defense-in-depth approach using Strapi's native security features and Node.js best practices.

Safe File Upload Implementation:

// Secure Strapi upload handler using safe libraries
const { pipeline } = require('stream');
const { promisify } = require('util');
const sharp = require('sharp'); // Safe image processing
const execa = require('execa'); // Safe command execution

const pipelineAsync = promisify(pipeline);

async safeUpload(file) {
  // Validate file type and size
  const allowedTypes = ['image/jpeg', 'image/png', 'image/webp'];
  if (!allowedTypes.includes(file.mimetype)) {
    throw new Error('Invalid file type');
  }
  
  if (file.size > 10 * 1024 * 1024) { // 10MB limit
    throw new Error('File too large');
  }
  
  // Use Sharp for safe image processing (no shell commands)
  const tempPath = `/tmp/${Date.now()}-${file.name}`;
  await file.mv(tempPath);
  
  try {
    const resizedBuffer = await sharp(tempPath)
      .resize(200, 200, { fit: 'inside' })
      .toBuffer();
    
    // Save processed file
    const uploadPath = `/uploads/${file.name}`;
    await pipelineAsync(
      resizedBuffer,
      require('fs').createWriteStream(uploadPath)
    );
    
    return uploadPath;
  } catch (error) {
    throw new Error('Image processing failed');
  }
}

Secure GraphQL Resolvers:

// Safe Strapi GraphQL resolver
module.exports = {
  Query: {
    systemInfo: async (_, args, { strapi }) => {
      // Only allow specific, safe operations
      if (args.action === 'getSystemInfo') {
        return {
          nodeVersion: process.version,
          platform: process.platform,
          memory: process.memoryUsage()
        };
      }
      
      throw new Error('Invalid action');
    }
  }
};

Plugin Security Hardening: Use Strapi's plugin validation system to restrict what plugins can do:

// strapi.config.js
module.exports = ({ env }) => ({
  // Disable dangerous plugin features
  pluginSettings: {
    upload: {
      provider: 'local',
      providerOptions: {
        uploadDir: './public/uploads',
        // Restrict file types and sizes at config level
        limits: {
          fileSize: 10 * 1024 * 1024,
          files: 5
        }
      }
    }
  },
  // Content Security Policy for admin panel
  policies: [
    'strapi::cors',
    'strapi::helmet',
    'strapi::rate-limit'
  ]
});

Runtime Protection: Deploy Strapi with proper container security controls:

# Secure Dockerfile for Strapi
FROM node:18-alpine

# Create non-root user
RUN addgroup -g 1001 -S nodejs && \
    adduser -S strapi -u 1001

WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

# Switch to non-root user
USER strapi

# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD curl -f http://localhost:1337/health || exit 1

EXPOSE 1337
CMD ["npm", "start"]