How to remediate – Network UPS Tools Cleartext Authentication

1. Introduction

Network UPS Tools is a suite of programs used for monitoring and managing uninterruptible power supplies. This vulnerability means that communication with the UPS isn’t encrypted, allowing attackers to intercept sensitive information. This affects servers responsible for reliable power management and could lead to credential theft and altered UPS settings. A successful attack could disrupt server availability, compromise data confidentiality, and impact system integrity.

2. Technical Explanation

The Network UPS Tools software does not enforce encrypted communication by default. This allows an attacker on the network to intercept traffic between the server and the UPS device. An attacker can then steal usernames and passwords used for management, potentially gaining full control of the UPS and any connected systems. The vulnerability exists because credentials are transmitted in cleartext.

• Root cause: Lack of enforced encryption for authentication data.
• Exploit mechanism: A man-in-the-middle attack intercepts communication between the server and the UPS, capturing usernames and passwords. Tools like Wireshark can be used to capture this traffic.
• Scope: Network UPS Tools versions that do not have StartTLS enabled are affected.

3. Detection and Assessment

You can check if your system is vulnerable by verifying the configuration of the upsd service, or by attempting to capture communication with the UPS.

• Quick checks: Check the upsd.conf file for the presence of the ‘CERTFILE’ directive. If it’s commented out or missing, encryption is likely disabled.
• Scanning: Nessus vulnerability ID 5a501865 can detect this issue. This should be used as an example only.
• Logs and evidence: Examine network traffic between the server and the UPS for cleartext credentials during authentication attempts.

grep CERTFILE /etc/upsd.conf

4. Solution / Remediation Steps

Enable StartTLS support on the server to encrypt communication with the UPS. This prevents attackers from intercepting sensitive information.

4.1 Preparation

• Take a backup of the upsd.conf file before making changes. Stop the upsd service if possible, though it may not be required depending on your configuration.
• Ensure you have a valid SSL certificate available for use with StartTLS. A roll back plan is to restore the original upsd.conf file and restart the service.
• A change window may be needed if stopping the UPS monitoring service impacts critical systems. Approval from the system owner might be required.

4.2 Implementation

1. Step 1: Edit the upsd.conf file and uncomment or add the ‘CERTFILE’ directive, pointing it to your SSL certificate path.
2. Step 2: Restart the upsd service for the changes to take effect.

4.3 Config or Code Example

Before

# CERTFILE = /etc/upsd/upsd.pem

After

CERTFILE = /etc/upsd/upsd.pem

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue. Using least privilege limits the impact if an attacker gains control. Secure defaults reduce the risk of misconfiguration. A regular patch cadence ensures you are running secure versions of software.

• Practice 1: Least privilege – restrict access to UPS management interfaces and credentials to only those who need it, reducing the potential damage from compromised accounts.
• Practice 2: Secure defaults – configure services with strong security settings by default, such as requiring encryption where available.

4.5 Automation (Optional)

If you manage your configuration using Ansible, you can automate this change.

---
- name: Enable StartTLS for Network UPS Tools
  hosts: all
  become: true
  tasks:
    - lineinfile:
        path: /etc/upsd.conf
        regexp: '^# CERTFILE'
        line: 'CERTFILE = /etc/upsd/upsd.pem'
        state: present
    - service:
        name: upsd
        state: restarted

5. Verification / Validation

Confirm the fix by checking the upsd.conf file and verifying that encrypted communication is now in use.

• Post-fix check: Run grep CERTFILE /etc/upsd.conf. The output should show a valid path to your SSL certificate.
• Re-test: Re-run the Nessus scan (ID 5a501865) and confirm that it no longer reports the vulnerability.
• Monitoring: Monitor logs for any errors related to SSL certificate validation or communication failures.

grep CERTFILE /etc/upsd.conf

6. Preventive Measures and Monitoring

Regularly update your security baselines to include secure configuration settings, such as enforcing encryption for sensitive services. Implement checks in your CI/CD pipelines to prevent insecure configurations from being deployed. A sensible patch or config review cycle will help catch issues like this quickly.

• Baselines: Update your server baseline with a requirement for StartTLS enabled on Network UPS Tools, referencing the relevant documentation.
• Pipelines: Add checks to your CI/CD pipeline that scan configuration files for missing or insecure settings.
• Asset and patch process: Review configurations every 3 months to ensure they remain secure.

7. Risks, Side Effects, and Roll Back

Enabling StartTLS requires a valid SSL certificate. Incorrectly configured certificates can cause communication failures. If issues occur, restore the original upsd.conf file.

• Risk or side effect 1: Invalid SSL certificate – causes communication errors and monitoring outages. Mitigation is to use a correctly signed certificate from a trusted CA.
• Risk or side effect 2: Service interruption – restarting the service may cause temporary loss of UPS monitoring. Mitigation is to schedule during off-peak hours.
• Roll back:
  1. Stop the upsd service.
  2. Restore the original upsd.conf file from backup.
  3. Restart the upsd service.

8. References and Resources

• Vendor advisory or bulletin: https://networkupstools.org/docs/user-manual.chunked/ar01s09.html
• NVD or CVE entry: Not applicable, this is a configuration issue rather than a specific software flaw.
• Product or platform documentation relevant to the fix: https://networkupstools.org/docs/user-manual.chunked/ar01s09.html