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Mitigation Strategies Analysis for sj26/mailcatcher

Mitigation Strategy: Network Isolation and Access Control (MailCatcher Configuration)

Mitigation Strategy: Restrict MailCatcher's Network Binding

Description:

  1. Identify MailCatcher's Startup Options: Examine how MailCatcher is started (e.g., command-line arguments, configuration file, Docker Compose).
  2. --http-ip and --smtp-ip: Use the --http-ip and --smtp-ip command-line options (or their equivalents in a configuration file) to explicitly bind MailCatcher to the localhost interface (127.0.0.1).
    • Example (Command-line): mailcatcher --http-ip=127.0.0.1 --smtp-ip=127.0.0.1
    • Example (Docker Compose, within the command section): 
      services:
  mailcatcher:
    image: sj26/mailcatcher
    command: --http-ip=127.0.0.1 --smtp-ip=127.0.0.1
    # ... other configurations ...
  3. Verification: After starting MailCatcher, use a network utility (e.g., netstat, ss) to confirm that it's only listening on 127.0.0.1.
    • Example (Linux): netstat -tulnp | grep mailcatcher (should only show 127.0.0.1)
  4. Firewall (Host-Level): Even with correct binding, add host-level firewall rules (iptables, ufw, Windows Firewall) to block all inbound connections to ports 1025 and 1080 except from 127.0.0.1. This provides a defense-in-depth layer.

Threats Mitigated:

  • Exposure of Sensitive Data (Severity: High): Prevents access to intercepted emails from other machines on the network.
  • Unintended Email Delivery (Severity: High): Reduces the risk of misconfiguration leading to external access.
  • Access Control Issues (Severity: High): Limits access to the MailCatcher interface.
  • Message Manipulation (Severity: Medium): Makes it harder for an attacker to access and modify emails.

Impact:

  • Exposure of Sensitive Data: Risk significantly reduced.
  • Unintended Email Delivery: Risk significantly reduced.
  • Access Control Issues: Risk significantly reduced.
  • Message Manipulation: Risk reduced.

Currently Implemented:

  • Yes/No/Partially: (Specify one)
  • Location: (e.g., MailCatcher startup script, Docker Compose file, firewall configuration)

Missing Implementation:

  • (e.g., "MailCatcher is currently binding to all interfaces (0.0.0.0).", "No firewall rules are in place to restrict access to MailCatcher's ports.")

Mitigation Strategy: Regularly Purge Emails (MailCatcher API)

Mitigation Strategy: Automated Email Purging via MailCatcher's API

Description:

  1. Script Creation: Write a script (e.g., Bash, Python) that uses the curl command (or a similar HTTP client) to send a DELETE request to MailCatcher's /messages API endpoint.
    • Example (Bash): 
      #!/bin/bash
MAILCATCHER_HOST="localhost"  # Or the hostname if using Docker
MAILCATCHER_PORT="1080"
curl -X DELETE http://$MAILCATCHER_HOST:$MAILCATCHER_PORT/messages
  2. Scheduling: Use a task scheduler (e.g., cron on Linux, Task Scheduler on Windows) to run this script at regular intervals (e.g., hourly, daily).
    • Example (cron - daily at 3:00 AM): 
      0 3 * * * /path/to/your/script.sh
  3. Error Handling: Add basic error handling to the script to check the HTTP response code and log any failures.
  4. Verification: After the script runs, check the MailCatcher web interface to confirm that the messages have been deleted.

Threats Mitigated:

  • Exposure of Sensitive Data (Severity: Medium): Reduces the window of opportunity for unauthorized access.
  • Denial of Service (DoS) (Severity: Low): Prevents MailCatcher from being overwhelmed.

Impact:

  • Exposure of Sensitive Data: Risk reduced.
  • Denial of Service (DoS): Risk minimized.

Currently Implemented:

  • Yes/No/Partially: (Specify one)
  • Location: (e.g., script file, cron job configuration)

Missing Implementation:

  • (e.g., "No automated purging is in place.", "Purging is done manually and infrequently.")

Mitigation Strategy: Reverse Proxy with Authentication (If Necessary)

Mitigation Strategy: Implement a reverse proxy (Nginx or Apache) with basic authentication in front of MailCatcher. This is only recommended if network isolation is absolutely impossible, and you must expose MailCatcher beyond localhost. Network isolation is always preferred.

Description:

  1. Choose a Reverse Proxy: Select either Nginx or Apache. Nginx is generally preferred for its performance and ease of configuration for this purpose.
  2. Install and Configure: Install the chosen reverse proxy on the same machine as MailCatcher (or a machine that can access MailCatcher).
  3. Configuration (Nginx Example): 
    server {
    listen 8080;  # Choose a port *different* from MailCatcher's default
    server_name mailcatcher.example.com; # Or an IP address

    location / {
        auth_basic "Restricted";
        auth_basic_user_file /etc/nginx/.htpasswd; # Path to htpasswd file
        proxy_pass http://127.0.0.1:1080; # Forward to MailCatcher
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}
  4. Create .htpasswd File: Use the htpasswd utility to create a username and password for accessing MailCatcher. 
    htpasswd -c /etc/nginx/.htpasswd yourusername
  5. Restart Nginx: Restart the Nginx service to apply the configuration.
  6. Access: Access MailCatcher through the reverse proxy's port (e.g., http://localhost:8080). You will be prompted for the username and password.
  7. Firewall: Configure your firewall to only allow access to the reverse proxy's port (8080 in this example), and block direct access to MailCatcher's port (1080).

Threats Mitigated:

  • Exposure of Sensitive Data (Severity: High): Adds a layer of authentication to prevent unauthorized access.
  • Access Control Issues (Severity: High): Requires credentials to access the MailCatcher interface.
  • Message Manipulation (Severity: Medium): Makes it harder for an attacker to access and modify emails.

Impact:

  • Exposure of Sensitive Data: Risk reduced, but network isolation is still strongly preferred.
  • Access Control Issues: Risk reduced.
  • Message Manipulation: Risk reduced.

Currently Implemented:

  • Yes/No/Partially: (Specify one)
  • Location: (e.g., Nginx configuration file, .htpasswd file)

Missing Implementation:

  • (e.g., "MailCatcher is directly accessible without authentication.", "No reverse proxy is configured.")