How to remediate – Active Connection to or from Host Listed in Custom Netstat IP …

1. Introduction

This report details the vulnerability “Active Connection to or from Host Listed in Custom Netstat IP …”. This means a system is communicating with an IP address that has been identified as potentially malicious based on custom netstat monitoring. This could indicate compromise, reconnaissance activity, or communication with command and control servers. Affected systems are typically any server or workstation performing network communications. A successful exploit could lead to data breaches, service disruption, or loss of confidentiality, integrity, and availability.

2. Technical Explanation

The vulnerability occurs when a host establishes an active TCP or UDP connection with an IP address present in a custom netstat threat list. This list is maintained by the administrator to identify known bad actors or suspicious IPs. The root cause is the lack of automated blocking or alerting on connections to/from these listed addresses. An attacker could exploit this by establishing communication with a compromised host within your network, using that host as a pivot point for further attacks. For example, an internal server connecting to a known command and control IP address suggests malware infection.

• Root cause: The system allows connections to/from IPs on the custom netstat threat list without blocking or alerting.
• Exploit mechanism: An attacker compromises a host and uses it to communicate with their infrastructure, triggering an alert based on the IP address being present in your custom netstat list.
• Scope: Any system configured with a custom netstat IP threat list is potentially affected.

3. Detection and Assessment

To confirm vulnerability, check current network connections against the custom netstat IP threat list. A quick check involves reviewing recent netstat output for matching IPs. A thorough method requires analyzing system logs for connection attempts to/from listed addresses over a longer period.

• Quick checks: Use `netstat -an` and manually compare the remote IP addresses against your custom threat list.
• Scanning: Nessus has identified this vulnerability through netstat analysis, providing an initial assessment.
• Logs and evidence: Review system logs (e.g., firewall logs, connection logs) for connections to/from IPs on the custom netstat threat list.

netstat -an | grep {IP address from your custom list}

4. Solution / Remediation Steps

The following steps outline how to remediate this issue. These steps focus on identifying and blocking connections to/from the listed IP addresses.

4.1 Preparation

• Dependencies: Access to firewall configuration or host-based security tools is required. Roll back plan: Restore previous configurations from backup.
• Change window needs: A short maintenance window may be required depending on the chosen remediation method and service impact. Approval from the network team may be needed.

4.2 Implementation

1. Step 1: Identify all systems with connections to/from IPs listed in your custom netstat threat list.
2. Step 2: Block outbound connections to those IP addresses at the firewall level.
3. Step 3: If possible, isolate affected hosts from the network for further investigation.
4. Step 4: Scan affected systems for malware or other indicators of compromise.

4.3 Config or Code Example

Before

# No firewall rule blocking connections to malicious IP address

After

# Firewall rule blocking outbound connection to malicious IP address
iptables -A OUTPUT -d {malicious_ip} -j DROP

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege limits the impact of compromised hosts. Input validation prevents malicious data from being processed. Patch cadence ensures systems are up-to-date with the latest security fixes.

• Practice 1: Implement least privilege to restrict network access for each host, reducing the potential damage if a system is compromised.
• Practice 2: Regularly update threat intelligence feeds and custom netstat lists to reflect current threats.

4.5 Automation (Optional)

# Example PowerShell script to block IPs in firewall
$IPList = @("192.168.1.10", "10.0.0.5") # Replace with your list
foreach ($IP in $IPList) {
  New-NetFirewallRule -DisplayName "Block Malicious IP: $IP" -Direction Outbound -RemoteAddress $IP -Action Block
}

5. Verification / Validation

Confirm the fix by verifying that connections to/from blocked IPs are no longer permitted. Re-run the initial detection method to confirm the issue is resolved. Perform a smoke test of key system functionalities.

• Post-fix check: Run `netstat -an` again and verify that connections to the blocked IP addresses are no longer present.
• Re-test: Re-run Nessus scan or manual netstat analysis to confirm the vulnerability is resolved.
• Monitoring: Monitor firewall logs for blocked connection attempts to/from listed IP addresses as a regression check.

netstat -an | grep {IP address from your custom list} # Should return no results

6. Preventive Measures and Monitoring

Update security baselines with the blocked IPs. Implement checks in CI/CD pipelines to prevent connections to known malicious IPs during deployment. Establish a regular patch and configuration review cycle.

• Baselines: Update your firewall baseline or policy to include blocking rules for known malicious IP addresses.
• Pipelines: Integrate threat intelligence feeds into your CI/CD pipeline to block deployments that connect to suspicious IPs.
• Asset and patch process: Review network configurations regularly (e.g., weekly) to ensure blocked IPs remain in place and are up-to-date.

7. Risks, Side Effects, and Roll Back

Blocking legitimate traffic is a potential risk if an IP address is incorrectly identified as malicious. Service disruptions may occur if critical services rely on communication with the blocked IPs. Restore previous configurations from backup to roll back changes.

• Risk or side effect 2: Service disruption – test blocking rules in a non-production environment first.
• Roll back: Restore the firewall configuration from the backup created prior to implementing the changes.

8. References and Resources

• Vendor advisory or bulletin: N/A – This is a custom threat list based on your own monitoring.
• NVD or CVE entry: N/A – No specific CVE associated with using a custom netstat IP list.
• Product or platform documentation relevant to the fix: Documentation for your firewall product regarding rule creation and management.