How to remediate – APC < 3.8.0 apcupsd Multiple Vulnerabilities

1. Introduction

The APC < 3.8.0 apcupsd Multiple Vulnerabilities affect systems running an older version of the apcupsd power management daemon. These vulnerabilities could allow a local attacker to crash the system or execute arbitrary code. This impacts confidentiality, integrity and availability. Systems commonly affected are Linux servers using UPS devices managed by apcupsd.

2. Technical Explanation

The apcupsd client has several security issues in versions prior to 3.8.0. These include a world-writable configuration file that allows process ID manipulation, an exploitable ‘log_event’ function and multiple buffer overflow vulnerabilities. An attacker could rewrite the PID file with malicious process IDs causing a denial of service or exploit code execution through buffer overflows. CVE-2001-0040 relates to the writable PID file issue.

• Root cause: The configuration file ‘/var/run/apcupsd.pid’ has insecure default permissions allowing any local user to modify it.
• Exploit mechanism: An attacker could rewrite the /var/run/apcupsd.pid file with a process ID they control, potentially causing apcupsd to crash or execute code in the context of another process. The buffer overflows allow remote attackers to send crafted packets that overwrite memory and gain control.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking the installed version of apcupsd. A thorough method involves reviewing logs for suspicious activity related to apcupsd.

• Quick checks: Run apcupsd -v to display the version number.
• Scanning: Nessus vulnerability ID 16897 may identify vulnerable systems, but can produce false positives.
• Logs and evidence: Check /var/log/syslog or /var/log/messages for apcupsd-related errors or unusual activity.

apcupsd -v

4. Solution / Remediation Steps

Upgrade to acpupsd version 3.8.0 or newer to fix the issue.

4.1 Preparation

• Back up your system before making changes. Stop the apcupsd service if possible: systemctl stop apcupsd.
• Ensure you have a method to restore the previous version if needed. A roll back plan is to revert to the backed-up configuration and restart the service.
• A change window may be required depending on your environment. Approval from system owners might be necessary.

4.2 Implementation

1. Step 1: Update the package list: sudo apt update (Debian/Ubuntu) or sudo yum update (CentOS/RHEL).
2. Step 2: Upgrade apcupsd: sudo apt install --only-upgrade apcupsd (Debian/Ubuntu) or sudo yum upgrade apcupsd (CentOS/RHEL).
3. Step 3: Verify the new version is installed using apcupsd -v.
4. Step 4: Restart the apcupsd service: systemctl start apcupsd.

4.3 Config or Code Example

Before

# Configuration file may have world-writable permissions

After

# Ensure /var/run/apcupsd.pid has appropriate permissions (e.g., 640) after upgrade. Check with ls -l /var/run/apcupsd.pid

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue.

• Practice 1: Least privilege – run services with the minimum necessary permissions to reduce impact if exploited.
• Practice 2: Patch cadence – regularly update software packages to address known vulnerabilities.

4.5 Automation (Optional)

# Example Ansible task to upgrade apcupsd
- name: Upgrade apcupsd package
  apt:
    name: apcupsd
    state: latest
  become: true

5. Verification / Validation

Confirm the fix by checking the version number and re-running earlier detection methods.

• Post-fix check: Run apcupsd -v and confirm the version is 3.8.0 or higher.
• Re-test: Re-run the Nessus scan to verify the vulnerability is no longer detected.
• Monitoring: Monitor /var/log/syslog for any new apcupsd errors or warnings.

apcupsd -v

6. Preventive Measures and Monitoring

Update security baselines and implement automated patch management to prevent similar issues.

• Baselines: Update your Linux server baseline to require apcupsd version 3.8.0 or higher.
• Asset and patch process: Implement a regular patch review cycle for all critical systems, including UPS management software.

7. Risks, Side Effects, and Roll Back

Upgrading apcupsd could potentially disrupt UPS monitoring if the configuration is incompatible with the new version.

• Roll back: Restore the backed-up configuration and restart the service to revert to the previous version.

8. References and Resources

• Vendor advisory or bulletin: http://www.novell.com/linux/security/advisories/2003_022_apcupsd.html
• NVD or CVE entry: https://nvd.nist.gov/vuln/detail/CVE-2001-0040
• Product or platform documentation relevant to the fix: https://www.apcupsd.com/