Crlf Injection in Restify with Api Keys

Crlf Injection occurs when user-controlled data is reflected in HTTP headers without proper sanitization, allowing an attacker to inject CRLF sequences (\r\n) to split headers and inject new ones. In Restify, when API keys are passed via request headers (e.g., x-api-key), and these values are used directly in custom header construction or logging, a Crlf Injection vector can emerge. For example, if an endpoint echoes the API key value into a response header without validation, an attacker can supply a key containing %0D%0A or literal \r\n sequences to inject headers such as Set-Cookie or X-Admin: true.

The risk is compounded because API keys are often treated as trusted identifiers; developers may assume header values are safe when they originate from an authenticated client. However, in an unauthenticated scan, middleBrick tests the attack surface without credentials, meaning it can probe endpoints that accept API keys in headers and reflect them. A crafted request like GET /resource?api_key=abc%0D%0ASet-Cookie:%20session=evil can cause the server to append an additional header if the application does not strip CR/LF characters. This can lead to response splitting, HTTP response smuggling, or bypass of security controls that rely on header integrity.

Using the OpenAPI/Swagger spec analysis feature, middleBrick cross-references definitions where API keys are declared (e.g., securitySchemes with type: apiKey) and checks runtime behavior for unsanitized reflection. Findings include whether the API key value appears in headers or logs and whether input validation permits newline characters. The scanner runs 12 security checks in parallel, including Input Validation and Data Exposure, to highlight whether Crlf Injection is present and to provide prioritized remediation guidance mapped to OWASP API Top 10 and relevant compliance frameworks.

To remediate Crlf Injection in Restify when handling API keys, ensure that any user-supplied data used in headers is sanitized by removing or encoding CR and LF characters. Below are concrete code examples demonstrating secure handling of API keys in Restify routes.

First, define a sanitization helper that strips carriage return and line feed characters:

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

Then, in your Restify server, apply this function before using the API key in any header logic:

const restify = require('restify');
const server = restify.createServer();

server.use((req, res, next) => {
  const apiKey = req.headers['x-api-key'] || '';
  const safeApiKey = sanitizeHeaderValue(apiKey);
  // Store the safe version for downstream use, do not forward the raw value
  req.context.apiKey = safeApiKey;
  return next();
});

server.get('/resource', (req, res, next) => {
  // Example: do not echo the API key directly into headers
  const customHeader = sanitizeHeaderValue(req.query.headerValue);
  if (customHeader) {
    res.setHeader('X-Custom', customHeader);
  }
  res.send({ keyPresent: !!req.context.apiKey });
  return next();
});

server.listen(8080, () => {
  console.log('Server listening on port 8080');
});

If you integrate with the middleBrick CLI (middlebrick scan <url>) or GitHub Action, you can validate that these sanitization patterns are in place and that your API security score improves. The Pro plan’s continuous monitoring can alert you if new endpoints introduce unsanitized header usage, and the dashboard helps track remediation over time.

Additionally, enforce strict validation on the format of API keys (e.g., allow only alphanumeric characters) at the schema level. For JSON-based APIs, use a library like Joi or express-validator to define and apply these rules consistently, reducing the attack surface for both Crlf Injection and other input-based flaws.