How to remediate – Zabbix Server Detection

1. Introduction

A Zabbix server is listening on the remote host, indicating a running instance of this open source network monitoring application. A Zabbix server collects data from monitored hosts using agents. This presents a potential risk as it expands the attack surface and could allow unauthorised access to monitoring data or potentially the server itself. Confidentiality, integrity, and availability may be impacted if compromised.

2. Technical Explanation

The Zabbix server process is running and listening for connections on a network port. Attackers can attempt to exploit vulnerabilities within the Zabbix software or gain access through misconfigurations. The primary risk is remote exploitation of known weaknesses in the Zabbix application itself.

• Root cause: The Zabbix server service is enabled and accessible on the network.
• Exploit mechanism: An attacker could attempt to exploit vulnerabilities in the Zabbix web interface or API, potentially leading to remote code execution or data theft. For example, an attacker might try to use a default credential or known vulnerability to gain access to the server’s configuration and monitoring data.
• Scope: All systems running any version of the Zabbix server are affected.

3. Detection and Assessment

Confirming whether a system is running a Zabbix server can be done with quick checks or thorough scanning methods.

• Quick checks: Use the netstat command to check for listening ports associated with Zabbix. For example, netstat -tulnp | grep zabbix will show any processes named ‘zabbix’ listening on TCP or UDP ports.
• Scanning: Nessus vulnerability scanner ID 16389 can detect running Zabbix servers. This is an example only and may require updating.
• Logs and evidence: Check system logs for entries related to the Zabbix server process, such as startup messages or error reports. Log files are typically located in /var/log/zabbix/.

netstat -tulnp | grep zabbix

4. Solution / Remediation Steps

The following steps outline how to limit access to the Zabbix server port, reducing potential exposure.

4.1 Preparation

• Ensure you have appropriate credentials for firewall management. A roll back plan is to restore the snapshot or restart the Zabbix server service.
• Changes should be made during a scheduled maintenance window with approval from IT security.

4.2 Implementation

1. Step 1: Configure the firewall to allow access only from trusted networks. For example, using iptables on Linux: sudo iptables -A INPUT -p tcp --dport 8080 -s / -j ACCEPT (replace with your actual port and network).
2. Step 2: Block all other incoming traffic to the Zabbix server port. For example, using iptables on Linux: sudo iptables -A INPUT -p tcp --dport 8080 -j DROP (replace with your actual port).
3. Step 3: Save the firewall rules to make them persistent across reboots. For example, using iptables-save > /etc/iptables/rules.v4 on Debian/Ubuntu.

4.3 Config or Code Example

Before

# No firewall rules for port 8080 (example)

After

sudo iptables -A INPUT -p tcp --dport 8080 -s / -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 8080 -j DROP

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate the risks associated with running a Zabbix server.

• Practice 1: Least privilege – restrict access to the Zabbix server and its data to only authorised users and systems.
• Practice 2: Network segmentation – isolate the Zabbix server on a separate network segment to limit the impact of potential compromises.

4.5 Automation (Optional)

#!/bin/bash
# Example Ansible playbook snippet to configure firewall rules for Zabbix server port 8080
- name: Allow access from trusted network
  iptables:
    chain: INPUT
    protocol: tcp
    dport: 8080
    source: /
    jump: ACCEPT
- name: Drop all other incoming traffic to port 8080
  iptables:
    chain: INPUT
    protocol: tcp
    dport: 8080
    jump: DROP

5. Verification / Validation

Confirm the fix by checking firewall rules and verifying access restrictions.

• Post-fix check: Use iptables -L INPUT | grep 8080 to confirm that the correct firewall rules are in place, allowing only traffic from trusted networks.
• Re-test: Run the initial netstat -tulnp | grep zabbix command and verify that access is restricted as expected.
• Smoke test: Ensure monitoring data continues to be collected from monitored hosts on the trusted network.
• Monitoring: Check firewall logs for blocked connections to port 8080 from untrusted sources. This can indicate attempted unauthorised access.

iptables -L INPUT | grep 8080

6. Preventive Measures and Monitoring

Regularly update security baselines and implement checks in CI/CD pipelines to prevent similar issues.

• Baselines: Update your network security baseline or policy to include specific firewall rules for Zabbix server ports.
• Asset and patch process: Implement a regular patch review cycle for the Zabbix server software to address known vulnerabilities promptly.

7. Risks, Side Effects, and Roll Back

Incorrectly configured firewall rules could block legitimate traffic.

• Risk or side effect 1: Blocking legitimate monitoring traffic – ensure that trusted networks are correctly defined in the firewall rules.
• Risk or side effect 2: Service disruption – incorrect rules may prevent Zabbix from functioning properly.
• Roll back: Step 1: Remove the added firewall rules using sudo iptables -D INPUT (replace with the rule number identified by iptables -L INPUT). Step 2: Restart the Zabbix server service if necessary.

8. References and Resources

• Vendor advisory or bulletin: https://www.zabbix.com/