Email Injection in Feathersjs with Dynamodb

Email Injection occurs when user-controlled input is concatenated into email headers or commands without validation, enabling an attacker to inject additional headers (e.g., CC, BCC, or newlines) or smuggled content. In a Feathersjs service that uses Dynamodb as the persistence layer, the risk arises when user-supplied data (such as email addresses, names, or message content) is passed to a mail transport or used to build DynamoDB item attributes that later feed into email generation.

Feathersjs is a JavaScript framework for building APIs quickly; it does not enforce strict input schema validation by default. If a service stores user data in Dynamodb and later uses that data in an email workflow (for example, sending notifications via SES or a third-party mailer), unsanitized fields like email or displayName can become injection vectors. An attacker might provide a payload such as email@example.com%0D%0BCC: attacker@example.com; if the application directly uses this value in a mail header or in a DynamoDB attribute that is later interpolated into email templates, injected headers can alter routing or disclose unintended recipients.

Because DynamoDB is a NoSQL database, injected newline or carriage-return characters may be stored verbatim and later retrieved for email assembly, preserving the injected structure. This becomes especially problematic when combined with server-side email generation that concatenates user data into headers. The unauthenticated scan capabilities of middleBrick can detect whether endpoints reflecting user-supplied email fields exhibit injection-prone patterns by analyzing input validation and output encoding across the unauthenticated attack surface.

Additionally, if the Feathersjs app exposes an endpoint that echoes stored email attributes in responses without proper encoding, an attacker may leverage injection to break out of JSON or HTML contexts when those attributes are consumed downstream. middleBrick’s LLM/AI Security checks do not apply here, but its standard validation and data exposure checks can highlight missing input sanitization and improper encoding that facilitate injection.

Remediation focuses on strict input validation, canonicalization, and safe usage of data when building emails or storing to DynamoDB. Below are concrete, realistic examples for a Feathersjs service using the AWS SDK for DynamoDB.

1. Validate and sanitize email input

Use a robust email validation library and reject or normalize inputs containing unexpected control characters. Ensure newlines and carriage returns are not allowed in email fields.

const validator = require('validator');
const sanitize = require('sanitize-html');

function safeEmail(rawEmail) {
  // Reject if contains newlines, tabs, or unexpected headers
  if (typeof rawEmail !== 'string' || !validator.isEmail(rawEmail)) {
    throw new Error('Invalid email');
  }
  // Remove hidden control characters
  return rawEmail.replace(/[\r\n\t]/g, '');
}

2. Use parameterized DynamoDB operations

Avoid string concatenation when constructing items. Use the AWS SDK’s native parameter structures to store email values safely, preventing accidental injection through attribute values.

const { DynamoDBClient, PutItemCommand } = require('@aws-sdk/client-dynamodb');
const client = new DynamoDBClient({ region: 'us-east-1' });

async function storeUser(email, displayName) {
  const safeEmail = safeEmail(email);
  const safeName = typeof displayName === 'string' ? displayName.replace(/[\r\n\t]/g, '') : '';

  const params = {
    TableName: 'Users',
    Item: {
      userId: { S: `user#${Date.now()}` },
      email: { S: safeEmail },
      displayName: { S: safeName },
      createdAt: { N: String(Date.now()) }
    }
  };
  await client.send(new PutItemCommand(params));
  return { email: safeEmail, displayName: safeName };
}

3. Encode when building email headers

When composing email headers, use header-safe encoding and avoid directly interpolating user input. For example, with Nodemailer and SES:

const nodemailer = require('nodemailer');
const sesTransport = require('nodemailer-ses-transport');

const transporter = nodemailer.createTransport(sesTransport({
  aws: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID,
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
    region: 'us-east-1'
  }
}));

async function sendNotification(toEmail, userDisplayName) {
  const safeTo = safeEmail(toEmail);
  const safeName = typeof userDisplayName === 'string' ? userDisplayName.replace(/[\r\n]/g, '') : 'User';

  const info = await transporter.sendMail({
    from: 'noreply@example.com',
    to: safeTo,
    subject: 'Account Notification',
    text: `Hello ${safeName},\n\nYour account has been updated.`
    // Do NOT build headers by concatenating user input
  });
  return info;
}

4. Centralize data retrieval and output encoding

When reading from DynamoDB and exposing data to email templates or API responses, encode based on context (HTML, JS string, URL). Do not trust stored values to be safe simply because they passed validation earlier.

async function getUserForEmailWorkflow(userId) {
  const params = {
    TableName: 'Users',
    Key: { userId: { S: userId } }
  };
  const cmd = new GetItemCommand(params);
  const { Item } = await client.send(cmd);
  if (!Item) return null;
  return {
    email: Item.email.S,
    displayName: Item.displayName?.S || ''
  };
}