Crlf Injection in Sails with Dynamodb

Crlf Injection occurs when user-controlled data is written into HTTP headers without proper sanitization, allowing an attacker to inject newline characters (CRLF / \r\n). In a Sails.js application using Amazon DynamoDB as a persistence layer, this typically happens when data stored in DynamoDB is later rendered in HTTP responses, such as in custom headers, cookies, or redirect URLs. Because DynamoDB is a NoSQL database, it does not enforce a schema, so developers may store raw input values directly. If those values are later used by Sails controllers or services to construct headers, an attacker can supply sequences like %0D%0A or literal \r\n to break out of the header context and inject additional headers or response body content.

In the Sails ecosystem, models often map directly to DynamoDB tables via an ORM or custom adapter. When user input flows from a DynamoDB record into a response header—such as setting res.set('X-Data', record.safariTrackingId)—unsanitized newline characters enable header manipulation. For example, an attacker who can control a DynamoDB attribute (e.g., a metadata field, custom tag, or redirect target) may inject Location: https://evil.com via CRLF, leading to response splitting, HTTP response smuggling, or open redirects. Because the scan testing methodology of middleBrick runs 12 security checks in parallel, including Input Validation and Data Exposure, it can detect whether response-splitting patterns are present when DynamoDB-sourced data reaches HTTP headers.

The risk is compounded when Sails actions directly forward DynamoDB attributes to clients without normalization. Consider a Sails controller that retrieves an item from DynamoDB and uses an attribute in a Set-Cookie header: if the attribute contains CRLF sequences, an attacker can inject additional Set-Cookie lines or other headers. MiddleBrick’s active testing includes header manipulation checks, highlighting how unchecked DynamoDB content can propagate into injection surfaces. Proper input validation and output encoding at the Sails layer are essential to prevent CRLF paths that originate in DynamoDB-stored data.

To mitigate CRLF Injection when using DynamoDB with Sails, sanitize and validate any data that may be used in HTTP headers, cookies, or redirects. Treat all DynamoDB attributes as untrusted, especially string fields that could contain carriage returns or line feeds. Implement a normalization layer in your Sails models or services that strips or encodes problematic characters before headers are set.

Example DynamoDB record retrieval and safe header usage in a Sails controller:

const sanitizeHeader = (value) => {
  if (typeof value !== 'string') return value;
  return value.replace(/[\r\n]+/g, '');
};

module.exports = {
  friendlyName: 'Get user profile',
  description: 'Retrieve user data from DynamoDB and set safe headers',
  inputs: {
    userId: { type: 'string', required: true }
  },
  exits: {
    serverError: { statusCode: 500 },
    notFound: { statusCode: 404 }
  },
  fn: async function (inputs, exits) {
    const dynamo = sails.helpers.aws.dynamodb;
    const params = {
      TableName: 'users',
      Key: { userId: { S: inputs.userId } }
    };

    let user;
    try {
      const result = await dynamo.get(params).promise();
      if (!result.Item) return exits.notFound();
      user = result.Item;
    } catch (err) {
      return exits.serverError(err);
    }

    // Safe usage: sanitize before header assignment
    const safeName = sanitizeHeader(user.name?.S || '');
    const safeEmail = sanitizeHeader(user.email?.S || '');

    res.set('X-User-Name', safeName);
    res.set('X-User-Email', safeEmail);

    return exits.success({
      id: user.userId?.S,
      name: safeName,
      email: safeEmail
    });
  }
};

Additionally, if you store redirect targets in DynamoDB, validate and restrict allowed origins before using them in responses:

const allowedOrigins = ['https://app.example.com', 'https://dashboard.example.com'];

const redirectUrl = user.redirectUrl?.S || '';
if (!allowedOrigins.some(origin => redirectUrl.startsWith(origin))) {
  return exits.serverError('Invalid redirect target');
}
res.redirect(redirectUrl);

For ongoing protection, integrate middleBrick’s CLI to scan endpoints from the terminal with middlebrick scan <url>, or add the GitHub Action to your CI/CD pipeline to fail builds if security scores drop below your threshold. These measures help catch header manipulation risks early, complementing runtime sanitization in Sails.