Attack Surface: 1. SMTP Authentication Bypass/Weakness
Description: Unauthorized sending of emails through Postal by bypassing or exploiting weak SMTP authentication. How Postal Contributes: Postal's core function is sending email via SMTP; its authentication mechanism is a direct and critical security control. Example: An attacker uses a brute-forced SMTP credential to send spam through the Postal server. Impact: Complete compromise of email sending; reputational damage; blacklisting. Risk Severity: Critical Mitigation Strategies: * Strong Password Policies: Enforce strong, unique passwords. * Multi-Factor Authentication (MFA): Implement MFA for SMTP. * Rate Limiting & Account Lockout: Prevent brute-force attacks. * Regular Credential Rotation: Rotate SMTP credentials. * IP Whitelisting: Restrict SMTP access to trusted IPs. * Disable Unused Authentication Methods: Remove weak authentication. * Security Audits: Audit the SMTP authentication code. * Monitor Logs: Watch for suspicious authentication activity.
Attack Surface: 2. Email Header Injection
Description: Manipulation of email headers to spoof senders or redirect replies.
How Postal Contributes: Postal directly constructs and sends emails, including headers. Flaws in its header handling are the vulnerability.
Example: An attacker adds a fake From header to impersonate a legitimate sender.
Impact: Phishing; data theft; reputational damage.
Risk Severity: High
Mitigation Strategies:
* Strict Input Validation: Validate/sanitize all data used for headers (whitelist approach).
* Encoding: Properly encode header values.
* Library Usage: Use well-vetted email libraries for header construction.
* Regular Expression Review: Carefully review regex used for validation.
* Testing: Test with malicious header inputs.
Attack Surface: 3. API Abuse (if applicable)
Description: Exploitation of Postal's API to send unauthorized emails or bypass limits. How Postal Contributes: If Postal has an API, that API's code is the direct attack surface. Example: A leaked API key is used to send spam, exceeding limits. Impact: Spam; reputational damage; resource exhaustion. Risk Severity: High (if an API exists) Mitigation Strategies: * Secure API Key Management: Treat API keys as highly sensitive. * API Key Rotation: Regularly rotate keys. * Rate Limiting (API-Specific): Strict rate limiting on API requests. * Input Validation (API): Validate all API input. * Authorization: Proper authorization for API users. * Auditing: Log all API requests. * Input Sanitization: Sanitize all data from the API.
Attack Surface: 4. Rate Limiting/Abuse Prevention Bypass
Description: Circumventing Postal's mechanisms to prevent sending excessive emails. How Postal Contributes: Postal should implement these; bypassing them is a direct attack on Postal's code. Example: Exploiting a flaw in rate limiting to send emails faster than allowed. Impact: Spam; denial-of-service; blacklisting. Risk Severity: High Mitigation Strategies: * Robust Rate Limiting: Use multiple factors (IP, sender, recipient). * IP Address Tracking: Track and throttle IPs. * Anomaly Detection: Identify unusual sending. * Regular Review: Adjust rate limiting rules.
Attack Surface: 5. Dependency Vulnerabilities
Description: Exploitation of vulnerabilities in third-party libraries used by Postal. How Postal Contributes: Postal directly depends on these libraries; their vulnerabilities become Postal's. Example: A vulnerable Ruby gem used by Postal allows code execution. Impact: Varies, but can be complete server compromise. Risk Severity: High to Critical Mitigation Strategies: * Regular Updates: Keep all dependencies up-to-date. * Vulnerability Scanning: Use scanners to find known issues. * Dependency Pinning: Pin versions (balance with updates). * Security Alerts: Subscribe to alerts for dependencies. * Least Privilege: Run Postal with minimal privileges.