How to remediate – apcnisd / apcupsd Detection

1. Introduction

The vulnerability is apcnisd / apcupsd Detection, where a UPS monitoring service is listening on a remote port. This allows potential attackers to access and potentially manipulate APC UPS devices connected to the network. Affected systems are typically those running APC power management software, which can impact confidentiality, integrity, and availability of connected devices.

2. Technical Explanation

The vulnerability stems from a daemon used to monitor and manage an APC UPS battery backup unit listening on a remote port. A lack of authentication or a flaw in the service itself may allow unauthorized access. An attacker could potentially turn off the devices plugged into the remote APC, causing downtime or data loss.

• Root cause: The apcupsd daemon listens for connections without strong authentication.
• Exploit mechanism: An attacker can connect to the service and send commands to control the UPS unit, potentially shutting it down.
• Scope: Systems running apcupsd are affected.

3. Detection and Assessment

To confirm if a system is vulnerable, check for the listening service and its version. A thorough method involves network scanning and review of running processes.

• Quick checks: Use `netstat -tulnp | grep apcupsd` to see if the service is listening on any ports.
• Scanning: Nessus plugin ID 16538 can detect this vulnerability, but results should be verified.
• Logs and evidence: Check system logs for apcupsd startup events or connection attempts.

netstat -tulnp | grep apcupsd

4. Solution / Remediation Steps

Restrict access to the port used by the UPS monitoring service to authorized hosts only. This prevents unauthorized control of connected devices.

4.1 Preparation

• A change window may be needed depending on your environment and impact assessment.

4.2 Implementation

1. Step 1: Identify the port apcupsd is listening on (e.g., using `netstat -tulnp | grep apcupsd`).
2. Step 2: Configure the firewall to allow access only from authorized hosts. For example, using `iptables` or `firewalld`.

4.3 Config or Code Example

Before

# No specific firewall rules for apcupsd port

After

iptables -A INPUT -p tcp --dport 3570 -s  -j ACCEPT
iptables -A INPUT -p tcp --dport 3570 -j DROP

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue, including least privilege and network segmentation.

• Practice 1: Least privilege – restrict access to services only from trusted sources.
• Practice 2: Network segmentation – isolate critical infrastructure like UPS devices on a separate network segment.

4.5 Automation (Optional)

# Example Ansible playbook snippet:
- name: Allow apcupsd access from authorized host
  iptables:
    chain: INPUT
    protocol: tcp
    dport: 3570
    source: 
    jump: ACCEPT
- name: Drop all other traffic to apcupsd port
  iptables:
    chain: INPUT
    protocol: tcp
    dport: 3570
    jump: DROP

5. Verification / Validation

Confirm the fix by verifying that only authorized hosts can connect to the UPS monitoring service. Perform a negative test from an unauthorized host.

• Post-fix check: Use `netstat -tulnp | grep apcupsd` and verify it’s still listening, but access is restricted.
• Re-test: Attempt to connect to the port from an unauthorized host; the connection should be refused.
• Smoke test: Verify that authorized hosts can still monitor the UPS status.
• Monitoring: Monitor firewall logs for blocked connections to the apcupsd port.

netstat -tulnp | grep apcupsd

6. Preventive Measures and Monitoring

Update security baselines and implement network monitoring to prevent similar issues in the future. For example, a CIS control or a GPO/Intune setting.

• Baselines: Update your firewall baseline to include rules for restricting access to critical services.
• Pipelines: Add checks in CI/CD pipelines to ensure that new systems are configured with appropriate firewall rules.
• Asset and patch process: Implement a regular review cycle of system configurations and security settings.

7. Risks, Side Effects, and Roll Back

Incorrectly configuring the firewall could block legitimate access to the UPS monitoring service. Ensure you have a clear roll back plan in place.

• Roll back: Remove the firewall rules added in Step 2 to restore default connectivity.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory found for this detection.
• NVD or CVE entry: No specific CVE found for this detection.
• Product or platform documentation relevant to the fix: APC Documentation