Email Injection with Basic Auth

Email injection in Basic Auth contexts typically occurs when authentication systems improperly handle email addresses containing malicious payloads. This vulnerability exploits the way Basic Auth processes credentials, particularly when email-based usernames are involved.

The most common attack vector involves credential stuffing attempts where attackers embed SQL injection or command injection payloads within email addresses. For example, an attacker might use:

admin@example.com' OR '1'='1

or

user@example.com; DROP TABLE users; --

These payloads exploit authentication middleware that concatenates email strings into database queries without proper sanitization. The Basic Auth header itself becomes the attack surface:

Authorization: Basic YW... (base64-encoded email:password)

Another manifestation occurs in logging and monitoring systems. When Basic Auth credentials containing email addresses are logged in plaintext (a common anti-pattern), email injection can corrupt log files or trigger log injection attacks. Consider this vulnerable logging pattern:

console.log(`Auth attempt from: ${email}`)

If the email contains newline characters or control sequences, it can break log formatting or inject malicious content.

Email injection also appears in password reset flows that use Basic Auth. An attacker might craft an email like:

victim@example.com%0ABcc: attacker@example.com

This exploits email header injection in password reset systems that construct email headers from Basic Auth credentials.

Detecting email injection in Basic Auth systems requires both static analysis and runtime scanning. The most effective approach combines automated scanning with manual code review of authentication middleware.

Runtime detection with middleBrick specifically targets Basic Auth endpoints by submitting crafted payloads through the Authorization header. The scanner tests for:

• SQL injection patterns in email fields
• Command injection attempts
• Log injection vectors
• Email header injection
• Cross-site scripting via error messages

Here's how middleBrick detects these issues in Basic Auth contexts:

middlebrick scan https://api.example.com/auth --basic-auth --test-email-injection

The scanner automatically decodes Base64 credentials, extracts email addresses, and tests them against a comprehensive payload library. It specifically looks for:

Manual detection should focus on authentication middleware code. Look for these anti-patterns:

// VULNERABLE: Direct string concatenation
const query = `SELECT * FROM users WHERE email='${email}' AND password='${password}'`;

Static analysis tools can flag these patterns, but runtime scanning with middleBrick provides empirical evidence of exploitability by actually testing the endpoint with malicious payloads.

Remediating email injection in Basic Auth systems requires a defense-in-depth approach. The most effective strategy combines input validation, secure coding practices, and proper error handling.

First, implement strict email validation before processing Basic Auth credentials. Use a comprehensive regex pattern that rejects suspicious characters:

function validateEmail(email) {
  const emailRegex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+  [a-zA-Z]{2,}$/;
  if (!emailRegex.test(email)) {
    throw new Error('Invalid email format');
  }
  // Additional checks for injection patterns
  if (email.includes(';') || email.includes('--') || email.includes('/*')) {
    throw new Error('Suspicious characters detected');
  }
  return true;
}

Next, use parameterized queries for any database operations involving email addresses:

// SECURE: Parameterized query
const query = 'SELECT * FROM users WHERE email = ? AND password = ?';
const [user] = await db.query(query, [email, password]);

This prevents SQL injection regardless of what's in the email field. For systems that must support legacy Basic Auth implementations, implement a sanitization layer:

function sanitizeEmail(email) {
  // Remove potentially dangerous characters
  return email.replace(/[';"\/*]/g, '');
}

For logging, use structured logging that treats email addresses as data fields rather than interpolated strings:

// SECURE: Structured logging
logger.info('Auth attempt', { email, timestamp: new Date().toISOString() });

This prevents log injection attacks. For email-based password reset systems, implement strict email header construction:

function sendPasswordReset(email) {
  const sanitizedEmail = sanitizeEmail(email);
  const mailOptions = {
    to: sanitizedEmail,
    subject: 'Password Reset',
    text: generateResetLink(sanitizedEmail)
  };
  await transporter.sendMail(mailOptions);
}

Finally, implement rate limiting and monitoring for Basic Auth endpoints to detect and block automated email injection attempts. Use middleBrick's continuous monitoring to ensure new vulnerabilities don't creep into your authentication system over time.