Information Disclosure in Fiber with Basic Auth

Information Disclosure in a Fiber application that uses HTTP Basic Authentication can occur when authentication credentials or related runtime details are inadvertently exposed through responses, error messages, or misconfigured middleware. In Fiber, which is a fast, unopinionated web framework built on fasthttp, developers often rely on Basic Auth for simplicity, but this convenience can lead to exposure of sensitive data when protections are incomplete.

Basic Authentication sends credentials in an Authorization header with the value Basic base64(username:password). While the header itself is not inherently insecure when transmitted over HTTPS, a Fiber app that does not explicitly enforce secure handling may leak credentials or metadata in several ways:

• Credentials may be logged inadvertently by application-level or server-level logging if request headers are captured without redaction.
• Error responses or stack traces might include the Authorization header value, especially if middleware does not sanitize inputs before generating diagnostic output.
• If the application exposes OpenAPI or debug endpoints that reflect the presence of Basic Auth, an attacker might infer authentication requirements or valid usernames through timing or enumeration.
• Without proper middleware to strip or ignore the Authorization header in certain contexts (e.g., static file serving or health checks), credentials could be returned in responses meant for unauthenticated clients.

These issues are not inherent to Basic Auth itself but arise from how the Fiber application integrates and exposes it. Because middleBrick tests the unauthenticated attack surface, it can detect whether responses include credentials, sensitive headers, or references to authentication mechanisms when they should not be present. This testing approach helps identify Information Disclosure risks specific to how Basic Auth is implemented in Fiber, such as missing header normalization, improper error handling, or insufficient transport security checks.

When combined with spec-driven analysis, middleBrick can correlate the declared use of Basic Auth in an OpenAPI definition with runtime behavior. For example, if the spec marks an endpoint as requiring basic security but the live endpoint returns a 401 without the proper WWW-Authenticate header or leaks credentials in error output, this inconsistency becomes a finding. Such findings highlight that the framework’s flexibility requires deliberate safeguards to prevent inadvertent information exposure.

To reduce Information Disclosure risks in Fiber when using Basic Authentication, implement explicit handling that prevents credentials from leaking through logs, errors, or unintended responses. Below are concrete remediation steps with code examples that you can apply in a Fiber application.

1. Use secure transport and avoid logging headers

Ensure that all routes requiring authentication are served over HTTPS. In Fiber, avoid logging incoming request headers indiscriminately. If logging is necessary, redact the Authorization header.

// Example: Redacting Authorization header in Fiber middleware
const loggerMiddleware = (c: Context) => {
  const authHeader = c.get('Authorization');
  const redactedHeader = authHeader ? 'Authorization: [redacted]' : 'Authorization: missing';
  console.log(`[${new Date().toISOString()}] ${c.method()} ${c.path()} ${redactedHeader}`);
  c.next();
};

app.use(loggerMiddleware);

2. Standardize WWW-Authenticate challenges

Always respond with a proper 401 Unauthorized and a WWW-Authenticate header using the Basic scheme. This prevents ambiguous error states that might disclose whether a username exists or how authentication is enforced.

// Example: Proper 401 WWW-Authenticate response in Fiber
const basicAuth = require('basic-auth');

app.get('/secure', (c, next) => {
  const user = basicAuth(c.req.raw);
  if (user == null || user.name !== 'admin' || user.pass !== 'correct-hashed-password') {
    c.set('WWW-Authenticate', 'Basic realm="FiberApp", charset="UTF-8"');
    c.status(401).send('Unauthorized');
    return;
  }
  next();
});

3. Avoid returning credentials in errors or responses

Ensure error handlers do not include raw request headers or authentication details. Use generic error messages and sanitize any middleware that might inadvertently include the Authorization header in output.

// Example: Safe error handler that avoids leaking headers
app.use((err, c, next) => {
  // Do not include req.headers in error output
  c.status(500).send({ error: 'Internal server error' });
});

4. Scope authentication to specific routes

Apply Basic Auth middleware only to routes that require protection, rather than globally, to minimize the surface area where headers might be exposed.

// Example: Applying Basic Auth selectively in Fiber
const auth = require('basic-auth');

const requireAuth = (c, next) => {
  const user = auth(c.req.raw);
  if (!user || !validCredentials(user)) {
    c.set('WWW-Authenticate', 'Basic realm="API"');
    c.status(401).end();
    return;
  }
  next();
};

app.get('/admin', requireAuth, (c) => {
  c.send('Admin area');
});

// Public routes remain unprotected
app.get('/health', (c) => {
  c.send('OK');
});

By combining these practices—redacting headers in logs, standardizing challenges, sanitizing errors, and scoping authentication—you reduce the likelihood of Information Disclosure in a Fiber application using Basic Auth. These steps align with secure handling patterns and help ensure that authentication-related metadata does not become an unintended attack surface.