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attack-surface.md

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Attack Surface Analysis for sj26/mailcatcher

Attack Surface: 1. Unintended Public Exposure

  • Description: MailCatcher's web interface (port 1080) or SMTP port (1025) are accessible from the public internet or a broader network than intended.
  • MailCatcher Contribution: MailCatcher's default configuration listens on all interfaces, making it vulnerable to accidental exposure if firewall rules or network configurations are not properly set.
  • Example: A developer deploys MailCatcher to a cloud server without configuring the cloud provider's security groups to restrict access. An attacker scans for open ports and finds MailCatcher running on port 1080.
  • Impact: Attackers can view all captured emails, potentially containing sensitive information (password resets, API keys, internal communications). They might also attempt to use the SMTP port for reconnaissance.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Network Segmentation: Use firewall rules (iptables, cloud security groups) to restrict access to MailCatcher's ports to only the local machine or a trusted development network.
    • VPN/SSH Tunneling: Require access via a VPN or SSH tunnel for any remote access.
    • Reverse Proxy with Authentication: Configure a reverse proxy (Nginx, Apache) with strong authentication (HTTP Basic Auth, OAuth) and authorization.
    • Configuration Audits: Regularly review network configurations and firewall rules.

Attack Surface: 2. Lack of Authentication/Authorization

  • Description: MailCatcher has no built-in authentication, allowing anyone with network access to view all captured emails.
  • MailCatcher Contribution: MailCatcher is designed for development and lacks authentication features by default.
  • Example: A developer shares a local network with others. Anyone on the network can access the MailCatcher interface and view emails.
  • Impact: Unauthorized access to emails, even within a trusted environment, can lead to information leakage.
  • Risk Severity: High (if exposed internally), Critical (if exposed publicly)
  • Mitigation Strategies:
    • Reverse Proxy with Authentication: Implement a reverse proxy (Nginx, Apache) with robust authentication and authorization. This is the primary mitigation.
    • Network Segmentation: Limit network access as described above.

Attack Surface: 3. Stored Cross-Site Scripting (XSS) via Email Content

  • Description: An attacker sends an email containing malicious JavaScript that is stored by MailCatcher and executed when a user views the email within the MailCatcher interface.
  • MailCatcher Contribution: MailCatcher displays email content, and if it doesn't properly sanitize this content, it can render malicious scripts.
  • Example: An attacker sends an email with a <script> tag in the body. When a developer views the email in MailCatcher, the script executes, potentially stealing cookies or redirecting the user.
  • Impact: Session hijacking (if authentication is added via a reverse proxy), defacement, or potentially gaining control of the user's browser.
  • Risk Severity: High
  • Mitigation Strategies:
    • Content Security Policy (CSP): Implement a strict CSP in MailCatcher (requires code modification) to restrict script sources.
    • Input Sanitization/Encoding: Ensure MailCatcher properly HTML-encodes email content (body and headers) before displaying it.
    • View as Plain Text: Configure MailCatcher or user behavior to prioritize viewing emails in plain text.
    • Regular Updates: Apply any security patches to MailCatcher if they become available.