Injection Flaws in Loopback

Remediating injection flaws in Loopback requires a defense-in-depth approach using the framework's built-in security features and proper input validation.

1. Use Parameterized Queries

Instead of string concatenation, use Loopback's query builder with parameterized queries:

// Vulnerable
const userId = ctx.query.id;
const sql = `SELECT * FROM users WHERE id = ${userId}`;

// Secure
const userId = ctx.query.id;
const sql = 'SELECT * FROM users WHERE id = ?';
const params = [userId];
const users = await app.dataSource.execute(sql, params);

2. Validate and Sanitize Filters

Implement strict filter validation in Loopback:

// Loopback 4 model with validated filters
import {Entity, model, property} from '@loopback/repository';

@model()
export class User extends Entity {
  @property({id: true}) id: number;
  @property() name: string;
  @property() email: string;
}

// Custom filter validator
export function validateUserFilter(filter: any) {
  const allowedOperators = ['$eq', '$gt', '$lt', '$in', '$nin'];
  
  function validate(obj: any): boolean {
    if (typeof obj !== 'object') return true;
    
    for (const [key, value] of Object.entries(obj)) {
      if (key.startsWith('$') && !allowedOperators.includes(key)) {
        return false;
      }
      if (typeof value === 'object' && !validate(value)) {
        return false;
      }
    }
    return true;
  }
  
  return validate(filter);
}

3. Use Loopback's Built-in Security Features

Loopback provides several security features that help prevent injection:

// Loopback 4 controller with injection prevention
import {inject} from '@loopback/core';
import {repository} from '@loopback/repository';
import {get, param, HttpErrors} from '@loopback/rest';
import {UserRepository} from '../repositories';

export class UserController {
  constructor(
    @repository(UserRepository) private userRepository: UserRepository,
  ) {}

  @get('/users/{id}', {
    responses: {
      '200': {
        description: 'User details',
        content: {'application/json': {schema: {'x-ts-type': User}}},
      },
    },
  })
  async findById(@param.path.number('id') id: number) {
    // Validate ID format
    if (!Number.isInteger(id) || id <= 0) {
      throw new HttpErrors.BadRequest('Invalid user ID format');
    }

    return await this.userRepository.findById(id);
  }

  @get('/users', {
    responses: {
      '200': {
        description: 'List of users',
        content: {'application/json': {schema: {'x-ts-type': [User]}}},
      },
    },
  })
  async findUsers(@param.query.object('filter', getFilterSchemaFor(User)) filter: object) {
    // Validate filter before use
    if (!validateUserFilter(filter)) {
      throw new HttpErrors.BadRequest('Invalid filter parameters');
    }
    
    return await this.userRepository.find(filter);
  }
}

4. Implement Content Security Policy

For Loopback applications that serve HTML, implement CSP headers:

// Loopback 4 sequence modification
import {DefaultSequence, FindRoute, InvokeMiddleware, ParseParams, Reject, RequestContext, Send, ServerResponse} from '@loopback/rest';

export class MySequence extends DefaultSequence {
  async handle(context: RequestContext) {
    const {request, response} = context;
    
    // Set CSP headers
    response.setHeader('Content-Security-Policy', "default-src 'self'; script-src 'self' 'nonce-...'; style-src 'self' 'unsafe-inline'");
    
    const route = this.findRoute(request);
    try {
      const args = await this.parseParams(request, route);
      const result = await this.invoke(route, args);
      this.send(response, result);
    } catch (error) {
      this.reject(context, route, error);
    }
  }
}

5. Use middleBrick for Continuous Monitoring

Integrate middleBrick into your CI/CD pipeline to catch injection vulnerabilities before deployment:

# .github/workflows/security.yml
name: Security Scan
on: [push, pull_request]

jobs:
  security-scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Install middleBrick
        run: npm install -g middlebrick
      - name: Scan API
        run: middlebrick scan https://staging-api.yourapp.com --fail-below B
        continue-on-error: true
      - name: Upload results
        uses: actions/upload-artifact@v2
        with:
          name: security-report
          path: middlebrick-report.json

This setup ensures that any new injection vulnerabilities are caught during development, preventing them from reaching production.