How to remediate – IPSEC Internet Key Exchange (IKE) Version 1 Detection

1. Introduction

The IPSEC Internet Key Exchange (IKE) Version 1 Detection vulnerability indicates a VPN server is listening on a remote port. This typically means a system is offering a way for remote users to connect securely into an internal network. A successful attack could allow unauthorised access to internal resources, potentially compromising confidentiality, integrity and availability of data.

2. Technical Explanation

The vulnerability occurs when a host enables Internet Key Exchange (IKE) version 1 for VPN connections. Attackers can attempt to negotiate an IKE/IPSEC connection with the server. Nessus detects this service by attempting to establish an IKE negotiation; if blocked, detection fails. This plugin does not operate over IPv6.

• Root cause: The remote host has IKE version 1 enabled.
• Exploit mechanism: An attacker could attempt to exploit weaknesses in the IKEv1 protocol or configuration to gain unauthorised access to the VPN server and, subsequently, internal network resources.
• Scope: Systems running VPN servers that support IKE version 1 are affected.

3. Detection and Assessment

You can confirm a system is vulnerable by checking for an active IKE listener. A thorough method involves attempting to establish an IKE connection from another host.

• Quick checks: Use netstat -an | grep :500 (or the equivalent on your OS) to check if port 500 is listening.
• Scanning: Nessus plugin ID 10428 can detect this vulnerability, but may not always be successful if blocked by firewalls or other security controls.
• Logs and evidence: Check firewall logs for connections attempts on UDP port 500.

netstat -an | grep :500

4. Solution / Remediation Steps

Disable the IKE service if it is not needed, or filter incoming traffic to this port.

4.1 Preparation

• Ensure you have access credentials for the server and understand the impact of disabling the VPN service. A roll back plan is to restore from the snapshot or restart the VPN service.
• A change window may be required depending on your organisation’s policies.

4.2 Implementation

1. Step 1: Disable the IKE service using the appropriate command for your operating system (e.g., systemctl stop ipsec or equivalent).
2. Step 2: Configure firewall rules to block incoming UDP traffic on port 500 if the service cannot be disabled.

4.3 Config or Code Example

Before

# ipsec.conf example (showing IKEv1 enabled)
config setup
  ike=yes
  ...

After

# ipsec.conf example (showing IKE disabled)
config setup
  ike=no
  ...

4.4 Security Practices Relevant to This Vulnerability

Least privilege and secure defaults are relevant practices for this vulnerability. Least privilege limits the impact if a VPN server is compromised. Secure defaults reduce the attack surface by disabling unnecessary services.

• Practice 1: Implement least privilege principles, granting only necessary access to VPN servers.
• Practice 2: Configure secure defaults on all systems, including disabling unused services like IKEv1.

4.5 Automation (Optional)

# Example PowerShell script to disable IKE service on remote machines
Invoke-Command -ComputerName $servers -ScriptBlock {
  Stop-Service -Name "IPSec" -Force
}

5. Verification / Validation

Confirm the fix by checking that port 500 is no longer listening and re-running the Nessus scan. A smoke test should verify basic VPN functionality if it’s still required.

• Post-fix check: Run netstat -an | grep :500; there should be no output.
• Re-test: Re-run Nessus plugin ID 10428 and confirm it no longer detects the vulnerability.
• Smoke test: If VPN is still needed, attempt a connection from a trusted client to verify functionality.
• Monitoring: Monitor firewall logs for any unexpected connections on UDP port 500 as an example of regression.

netstat -an | grep :500

6. Preventive Measures and Monitoring

Update security baselines to include disabling IKEv1 by default, and add checks in CI/CD pipelines to enforce this setting. A regular patch cycle ensures systems are up-to-date with the latest security fixes.

• Baselines: Update your system baseline or policy to disable IKE version 1 unless specifically required.
• Pipelines: Add a check in your CI/CD pipeline to ensure that IKEv1 is disabled on all new systems.
• Asset and patch process: Implement a regular patch review cycle for all VPN servers.

7. Risks, Side Effects, and Roll Back

Disabling the IKE service will prevent any VPN connections using IKE version 1. Ensure you have alternative VPN solutions in place if needed. To roll back, re-enable the IKE service and restore firewall rules.

• Risk or side effect 1: Disabling IKEv1 may break existing VPN connections.
• Roll back: Step 1: Re-enable the IKE service using systemctl start ipsec (or equivalent). Step 2: Restore firewall rules to allow incoming UDP traffic on port 500 if previously blocked.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory available in the context provided.
• NVD or CVE entry: No specific CVE entry available in the context provided.
• Product or platform documentation relevant to the fix: No specific product documentation available in the context provided.