How to remediate – StoneGate Firewall Client Authentication Detection

1. Introduction

The StoneGate Firewall Client Authentication Detection vulnerability indicates a StoneGate firewall client is installed on a remote host. This service should not be directly accessible from the internet or non-administrative internal networks as it presents an attack surface. Affected systems are typically those where StoneGate firewalls are used and clients have been deployed for remote access or VPN functionality. A successful exploit could allow unauthorised access to the network. Confidentiality, integrity, and availability may all be impacted if exploited.

2. Technical Explanation

This vulnerability occurs because the StoneGate firewall client login service is exposed in a way that allows remote connections. An attacker can attempt to authenticate to this service directly, potentially gaining access to internal network resources. There is no known CVE associated with this specific detection; it represents a configuration issue rather than a software flaw. An example attack would involve an attacker attempting a brute-force login against the exposed client service from an external IP address.

• Root cause: The StoneGate firewall client authentication service is accessible from untrusted networks, bypassing intended security controls.
• Exploit mechanism: An attacker attempts to connect to the client service and uses valid or guessed credentials to gain access. A simple example payload would be a standard username/password login attempt using tools like Nmap’s smb-auth script.
• Scope: Systems running StoneGate firewall clients, particularly those configured for remote access. Affected versions depend on the client software installed but are generally applicable across all supported releases if not properly restricted.

3. Detection and Assessment

Confirming vulnerability involves checking network accessibility to the client service and identifying exposed instances. A quick check can verify running processes, while a thorough scan assesses open ports.

• Quick checks: Use `netstat -an | grep ` (replace `` with the StoneGate client port) to see if the service is listening on an external interface.
• Scanning: Nessus plugin ID 16725 can identify exposed StoneGate firewall clients, but results should be verified manually.
• Logs and evidence: Check firewall logs for connections to the StoneGate client authentication port (default is often UDP 500). Event IDs will vary depending on the specific firewall configuration.

netstat -an | grep 500

4. Solution / Remediation Steps

Fixing this issue involves restricting incoming traffic to the StoneGate client authentication port, limiting access only to trusted networks.

4.1 Preparation

• Dependencies: Ensure no legitimate remote access users are affected by restricting traffic. Roll back plan: Restore the firewall configuration from the pre-change snapshot.
• Change window needs: Changes should be made during a scheduled maintenance window with approval from the network security team.

4.2 Implementation

1. Step 1: Create a new firewall rule to deny incoming traffic to the StoneGate client authentication port (e.g., UDP 500) from all networks except trusted internal subnets.
2. Step 3: Verify the new rule is active and blocking traffic from untrusted sources using a test connection attempt from an external IP address.

4.3 Config or Code Example

Before

# Allow all traffic to StoneGate client port (example)
allow tcp any any 500
allow udp any any 500

After

# Deny all traffic from untrusted networks
deny tcp any  500
deny udp any  500
# Allow only trusted internal networks
allow tcp  any 500
allow udp  any 500

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.

• Practice 1: Least privilege – restrict network access to the minimum required for legitimate operations, reducing the attack surface.
• Practice 2: Network segmentation – isolate sensitive services like firewall clients on separate networks with strict access controls.

4.5 Automation (Optional)

If suitable, provide a small script or infrastructure code that applies the fix at scale. Only include if safe and directly relevant.

# Example Ansible snippet to deny traffic from untrusted networks (example only - adapt for your environment)
- name: Deny StoneGate client access from untrusted network
  firewalld:
    zone: public
    rule: reject
    port: 500/udp
    source: 
    permanent: true
  become: yes

5. Verification / Validation

Confirming the fix involves verifying that traffic is blocked from untrusted networks and legitimate access remains functional.

• Post-fix check: Run `netstat -an | grep 500` again; it should only show listening connections on trusted interfaces.
• Re-test: Re-run the earlier scan (Nessus plugin ID 16725) and confirm that exposed instances are no longer reported.
• Smoke test: Verify remote access users can still connect to the network using the StoneGate client from a trusted internal IP address.
• Monitoring: Monitor firewall logs for blocked connection attempts to port 500 from untrusted sources as an example alert.

netstat -an | grep 500

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type.

• Baselines: Update security baselines or policies to enforce strict network access controls for all firewall clients, such as a CIS control related to firewall configuration.
• Pipelines: Add checks in CI/CD pipelines to validate firewall rules and ensure that unnecessary ports are not exposed.
• Asset and patch process: Implement a regular review cycle (e.g., quarterly) of firewall configurations to identify and remediate misconfigurations like this one.

7. Risks, Side Effects, and Roll Back

List known risks or service impacts from the change.

• Risk or side effect 1: Blocking legitimate traffic if trusted networks are incorrectly configured; mitigate by carefully defining trusted network ranges.
• Risk or side effect 2: Service interruption for remote access users if changes are not tested thoroughly; mitigate with phased deployment and monitoring.
• Roll back: Restore the firewall configuration from the pre-change snapshot taken in step 4.1.

8. References and Resources

Link only to sources that match this exact vulnerability.

• Vendor advisory or bulletin: Check StoneGate’s support portal for relevant security advisories regarding firewall client configuration best practices.
• NVD or CVE entry: As this is a configuration issue, there is no specific NVD/CVE entry.
• Product or platform documentation relevant to the fix: Refer to the StoneGate Firewall Administration Guide for details on configuring firewall rules and network access controls.