CVE-2021-27025: Puppet Agent DOS Vulnerability

CVE-2021-27025 Overview

A flaw was discovered in Puppet Agent where the agent may silently ignore Augeas settings or may be vulnerable to a Denial of Service condition prior to the first 'pluginsync'. This vulnerability affects the configuration management workflow and can lead to service disruption in enterprise environments running Puppet infrastructure.

Critical Impact

Puppet Agent installations may silently fail to apply Augeas configuration settings or become unresponsive due to DoS conditions, potentially leaving systems in an inconsistent or unmanaged state prior to the initial pluginsync operation.

Affected Products

• Puppet Enterprise
• Puppet Agent
• Fedora 35 (via packaged Puppet components)

Discovery Timeline

• 2021-11-18 - CVE-2021-27025 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-27025

Vulnerability Analysis

This vulnerability occurs in Puppet Agent during the initial configuration phase before the first 'pluginsync' operation completes. The flaw manifests in two potential ways: either Augeas settings are silently ignored without proper error reporting, or the agent becomes susceptible to a Denial of Service condition.

Augeas is a configuration editing tool used by Puppet to manage configuration files in a structured manner. When Augeas settings are silently ignored, configuration changes intended by administrators may not be applied, leaving systems in an unintended state. The Denial of Service aspect can render the Puppet Agent unresponsive, preventing configuration management operations from executing.

The network-based attack vector requires low privileges but no user interaction, making it exploitable by authenticated attackers with network access to affected Puppet infrastructure. The primary impact is on availability, as configuration management services may become disrupted.

Root Cause

The root cause relates to how Puppet Agent handles Augeas-related operations during the initialization phase before pluginsync completes. During this window, the agent's handling of Augeas settings contains a flaw that can either suppress error conditions (causing silent failures) or allow resource exhaustion leading to service unavailability.

Attack Vector

The vulnerability is exploitable over the network by an attacker with low-level privileges. The attack does not require user interaction and targets the Puppet Agent's initialization and configuration parsing mechanisms. An attacker could exploit this flaw to either cause configuration drift by ensuring Augeas settings are ignored, or to disrupt Puppet infrastructure operations through Denial of Service.

The exploitation window exists specifically during the period before the first pluginsync operation completes, which is when the Puppet Agent synchronizes plugins from the Puppet Server.

Detection Methods for CVE-2021-27025

Indicators of Compromise

• Unexpected Puppet Agent service crashes or hangs during initialization
• Configuration files managed by Augeas remaining unchanged despite expected modifications
• Error logs showing abnormal behavior during the pre-pluginsync phase
• Increased resource consumption on systems running Puppet Agent

Detection Strategies

• Monitor Puppet Agent logs for errors or warnings related to Augeas operations during agent startup
• Implement configuration drift detection to identify when Augeas-managed files deviate from expected states
• Deploy health checks that verify Puppet Agent responsiveness during and after initialization
• Review system logs for Puppet Agent service restarts or crashes

Monitoring Recommendations

• Configure alerting on Puppet Agent service availability and response times
• Establish baseline metrics for Puppet Agent initialization timing to detect anomalies
• Monitor for configuration inconsistencies between intended and actual system states
• Track pluginsync operation completion across managed infrastructure

How to Mitigate CVE-2021-27025

Immediate Actions Required

• Update Puppet Agent to the latest patched version available from Puppet
• Review Puppet Enterprise deployments and apply vendor-recommended security patches
• Verify Augeas configuration settings are being applied correctly after patching
• Monitor Puppet Agent health closely during the upgrade process

Patch Information

Puppet has released security updates to address this vulnerability. Administrators should consult the Puppet Security Advisory for CVE-2021-27025 for specific version information and upgrade guidance. Fedora users should refer to the Fedora Package Announcement for distribution-specific updates.

Workarounds

• Ensure Puppet Agent has completed pluginsync before relying on Augeas-managed configurations
• Implement network segmentation to limit access to Puppet infrastructure from untrusted networks
• Consider temporarily increasing monitoring and validation of configuration changes during the pre-pluginsync window
• Apply principle of least privilege to accounts with access to Puppet infrastructure

# Verify Puppet Agent version after patching
puppet --version

# Check Puppet Agent service status
systemctl status puppet

# Review recent Puppet Agent logs for anomalies
journalctl -u puppet --since "1 hour ago" | grep -i augeas