How to remediate – UMN Gopherd Unauthorized FTP Proxy

1. Introduction

UMN Gopherd Unauthorized FTP Proxy is a flaw in UMN Gopher servers that allows them to act as an open proxy for FTP connections. This means attackers can use your server to connect to other FTP sites, hiding their own IP address and potentially bypassing network restrictions. Systems running a UMN Gopher server with FTP support enabled are usually affected. A successful exploit could lead to information disclosure, network reconnaissance, or the ability to access resources on internal networks. Confidentiality, integrity, and availability may be impacted.

2. Technical Explanation

The vulnerability occurs because the Gopher server does not properly restrict connections initiated through FTP requests. When a user sends an ‘ftp://hostname.of.the.ftp.server’ request, the server attempts to connect to that host as a proxy. This allows an attacker to relay traffic through your server. Exploitation requires a publicly accessible UMN Gopher server with FTP support enabled.

• Root cause: The Gopher daemon lacks sufficient input validation and access controls when handling FTP proxy requests.
• Exploit mechanism: An attacker sends a specially crafted request to the Gopher server, initiating an FTP connection to a target host. For example, sending ‘ftp://example.com’ would attempt to connect to example.com via your Gopher server.
• Scope: Affected platforms are those running a UMN Gopher daemon with proxy functionality enabled. Specific versions were not specified in the provided information.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking its Gopher server configuration and listening ports. A thorough assessment involves attempting to connect through the server as an FTP proxy.

• Quick checks: Use netstat to check for open ports associated with the Gopher daemon (typically port 70) and any related FTP connections.
• Scanning: Nessus plugin ID 6782 may identify this vulnerability. This is provided as an example only.
• Logs and evidence: Check Gopher server logs for connection attempts to external FTP hosts. Log file locations vary depending on the installation, but common paths include /var/log/gopherd or similar.

netstat -tulnp | grep gopherd

4. Solution / Remediation Steps

The recommended solution is to disable FTP support in the remote Gopher server.

4.1 Preparation

4.2 Implementation

1. Step 1: Edit the Gopher server configuration file (typically gopherd.conf).
2. Step 2: Locate the option controlling FTP proxy support and disable it. This may involve setting a value to ‘no’ or commenting out the relevant line.
3. Step 3: Save the changes to the configuration file.
4. Step 4: Restart the Gopher service to apply the new configuration.

4.3 Config or Code Example

Before

ftp_proxy on

After

ftp_proxy off

4.4 Security Practices Relevant to This Vulnerability

List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.

• Practice 1: Least privilege – running services with minimal necessary permissions reduces the impact if exploited.
• Practice 2: Safe defaults – disabling unnecessary features like FTP proxy support by default prevents accidental exposure.

4.5 Automation (Optional)

# Example Bash script (use with caution)
# Replace /etc/gopherd.conf with your actual config file path
sed -i 's/ftp_proxy on/ftp_proxy off/' /etc/gopherd.conf
systemctl restart gopherd

5. Verification / Validation

Confirm the fix by checking the Gopher server configuration and attempting to connect through it as an FTP proxy.

• Post-fix check: Use netstat again to confirm that no ports associated with FTP connections are open.
• Re-test: Attempt to initiate an FTP connection via the Gopher server using a client (e.g., `ftp://your_server`). The connection should fail.
• Smoke test: Verify that other Gopher functionality still works as expected. For example, accessing simple text files.
• Monitoring: Monitor Gopher server logs for any unexpected FTP-related activity. Look for error messages indicating failed connection attempts.

netstat -tulnp | grep gopherd

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type. Use “for example” to keep advice conditional, not prescriptive.

• Baselines: Update your security baseline or policy to include a requirement for disabling unnecessary features in all services (for example, CIS control 5.1).
• Pipelines: Add checks in CI/CD pipelines to ensure that configuration files adhere to the security baseline.
• Asset and patch process: Implement a regular review cycle for service configurations to identify and address potential vulnerabilities.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Disabling FTP proxy support may break existing functionality if it is actively used.
• Risk or side effect 2: Incorrect configuration changes could prevent the Gopher server from starting.
• Roll back: Restore the original Gopher server configuration file and restart the service.

8. References and Resources

• Vendor advisory or bulletin: SecurityFocus BID 6782
• NVD or CVE entry: No CVE was specified in the provided information.
• Product or platform documentation relevant to the fix: Documentation for UMN Gopherd is not publicly available as of this writing.