How to remediate – SOCKS Server Detection

1. Introduction

A SOCKS server is running on this host. A SOCKS (SOCKetS) server allows applications to connect through a firewall, potentially exposing internal services. This matters because it could allow unauthorised access to your network if not properly secured. Affected systems are typically those providing proxy or tunnelling functionality. Impact on confidentiality, integrity and availability depends on the configuration of the SOCKS server itself.

2. Technical Explanation

The remote service is a SOCKS server which enables client applications to operate transparently through firewalls. Exploitation involves connecting to the exposed SOCKS server and using it as an intermediary to access internal resources. Preconditions include network connectivity to the SOCKS server port, typically 1080 or 1081. An attacker could use a SOCKS proxy tool to tunnel traffic through your firewall and reach services that should not be directly accessible from the internet. Affected platforms are any operating system supporting SOCKS implementations, such as Linux, Windows, and macOS.

• Root cause: The presence of an active SOCKS server service listening on a network interface.
• Exploit mechanism: An attacker connects to the SOCKS server using a client application configured to use it as a proxy. They then attempt to access internal resources through this connection. For example, connecting to an internal database or web server.
• Scope: Any system running a SOCKS server implementation (e.g., Dante, 3proxy).

3. Detection and Assessment

Confirming the presence of a SOCKS server can be done with network scanning tools or by checking listening ports. A thorough method involves analysing the service configuration file.

• Quick checks: Use `netstat -tulnp` on Linux to list listening ports and associated processes. Look for entries on port 1080 or 1081.
• Scanning: Nessus plugin ID 34759 can detect SOCKS server detection. This is an example only.
• Logs and evidence: Check system logs for the startup of SOCKS server processes (e.g., Dante, 3proxy). Log files are typically located in /var/log or similar directories depending on the distribution.

netstat -tulnp | grep ':1080|:1081'

4. Solution / Remediation Steps

The following steps outline how to disable or secure a SOCKS server. Only apply these steps if the SOCKS server is not required for legitimate business purposes.

4.1 Preparation

• Ensure you have access to restart the service if needed. A roll back plan is to restore from the snapshot or restart the service with its original configuration.
• Change windows should be planned during off-peak hours and approved by the IT security team.

4.2 Implementation

1. Step 1: Stop the SOCKS server service using `systemctl stop ` (e.g., `systemctl stop dante`).
2. Step 2: Disable the SOCKS server service from starting automatically on boot with `systemctl disable ` (e.g., `systemctl disable dante`).
3. Step 3: Remove the SOCKS server package if it is not required using your system’s package manager (e.g., `apt remove dante` or `yum remove dante`).

4.3 Config or Code Example

Before

# /etc/danted.conf
internal: 192.168.1.0/24 port=1080
external: eth0
socksmethod: username none
logoutput: syslog

After

# /etc/danted.conf (commented out all lines)
#internal: 192.168.1.0/24 port=1080
#external: eth0
#socksmethod: username none
#logoutput: syslog

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege limits the impact if a SOCKS server is compromised. Network segmentation isolates internal resources from external access.

• Practice 1: Least privilege – only allow necessary services to run and limit their network access.
• Practice 2: Network segmentation – isolate sensitive systems behind firewalls and restrict access based on the principle of least privilege.

4.5 Automation (Optional)

#!/bin/bash
# Script to stop and disable Dante SOCKS server on multiple systems
for host in $(cat /path/to/hostlist); do
  ssh $host "sudo systemctl stop dante"
  ssh $host "sudo systemctl disable dante"
done

5. Verification / Validation

Confirm the fix by checking that the SOCKS server is no longer listening on any ports and verifying service status. A smoke test should confirm other network services are still functioning correctly.

• Post-fix check: Run `netstat -tulnp | grep ‘:1080|:1081’`. Expected output should be empty.
• Re-test: Re-run the earlier detection method (e.g., Nessus plugin ID 34759) to confirm it no longer detects a SOCKS server.
• Smoke test: Verify that other network services, such as SSH and web servers, are still accessible.
• Monitoring: Monitor system logs for any attempts to start the SOCKS service. Example query: `grep -i ‘dante’ /var/log/syslog`.

netstat -tulnp | grep ':1080|:1081'

6. Preventive Measures and Monitoring

Update security baselines to prevent unnecessary services from running. Implement CI/CD pipeline checks to identify rogue SOCKS server installations.

• Baselines: Update your system baseline or CIS control settings to disallow the installation of unauthorized proxy servers.
• Pipelines: Add static analysis (SAST) tools to your CI/CD pipeline to detect configuration files associated with SOCKS servers during build time.
• Asset and patch process: Review server configurations regularly, at least quarterly, to ensure compliance with security policies.

7. Risks, Side Effects, and Roll Back

Disabling a SOCKS server may impact applications that rely on it for proxy functionality. Rolling back involves restarting the service with its original configuration.

• Risk or side effect 1: Applications relying on the SOCKS server will be unable to connect through it. Mitigation is to restore the service and configure it correctly.
• Roll back: Step 1: Start the SOCKS server service using `systemctl start ` (e.g., `systemctl start dante`). Step 2: Verify that the service is running correctly and accessible.

8. References and Resources

• Vendor