CVE-2020-1742: Nmstate Kubernetes Privilege Escalation Flaw

CVE-2020-1742 Overview

An insecure modification vulnerability flaw was found in containers using nmstate/kubernetes-nmstate-handler. An attacker with access to the container could use this flaw to modify /etc/passwd and escalate their privileges. This vulnerability affects versions before kubernetes-nmstate-handler-container-v2.3.0-30.

Critical Impact

Local attackers with container access can escalate privileges by modifying /etc/passwd, potentially gaining root-level access within the container environment.

Affected Products

• nmstate kubernetes-nmstate (versions before v2.3.0-30)
• Red Hat OpenShift Virtualization 2

Discovery Timeline

• 2021-06-07 - CVE-2020-1742 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-1742

Vulnerability Analysis

This vulnerability is classified under CWE-266 (Incorrect Privilege Assignment) and CWE-732 (Incorrect Permission Assignment for Critical Resource). The flaw exists in the kubernetes-nmstate-handler container image, which is used for managing network configurations in Kubernetes environments.

The root issue stems from improper file permission configurations within the container, allowing unprivileged processes to modify sensitive system files. In containerized environments, proper isolation and permission controls are critical to prevent lateral movement and privilege escalation attacks.

Root Cause

The vulnerability arises from insecure permission settings on the /etc/passwd file within the kubernetes-nmstate-handler container. The container image was built with overly permissive file access controls, failing to properly restrict write access to critical system files. This misconfiguration allows any process running inside the container with local access to modify user account information.

Attack Vector

The attack requires local access to the affected container. An attacker who has gained initial access to the container (through another vulnerability, misconfiguration, or legitimate access) can exploit this flaw to escalate privileges.

The exploitation process involves:

1. Attacker gains initial access to the kubernetes-nmstate-handler container
2. Attacker identifies that /etc/passwd has insecure write permissions
3. Attacker modifies /etc/passwd to add a new user with root privileges or modify an existing user's privilege level
4. Attacker escalates to root or another privileged account within the container

This type of attack is particularly concerning in Kubernetes environments where containers may have access to sensitive cluster resources or host system components.

Detection Methods for CVE-2020-1742

Indicators of Compromise

• Unexpected modifications to /etc/passwd within kubernetes-nmstate-handler containers
• New user accounts appearing in container user databases
• Unusual privilege levels assigned to existing container users
• Process execution by unexpected user accounts within affected containers

Detection Strategies

• Monitor file integrity of /etc/passwd within kubernetes-nmstate-handler containers using tools like AIDE or Tripwire
• Implement container runtime security monitoring to detect unauthorized file modifications
• Review container image versions and verify they are patched beyond v2.3.0-30
• Use Kubernetes admission controllers to prevent deployment of vulnerable container versions

Monitoring Recommendations

• Enable audit logging for file system operations within container environments
• Configure alerts for any write operations to sensitive system files in containers
• Implement behavioral analysis to detect privilege escalation patterns
• Monitor container user account changes through centralized logging

How to Mitigate CVE-2020-1742

Immediate Actions Required

• Update kubernetes-nmstate-handler containers to version v2.3.0-30 or later
• Audit existing container deployments to identify vulnerable versions
• Review container security policies and enforce least-privilege principles
• Restrict access to containers to only authorized personnel and processes

Patch Information

The vulnerability is fixed in kubernetes-nmstate-handler-container-v2.3.0-30 and later versions. Organizations using Red Hat OpenShift Virtualization should consult Red Hat Bug Report #1803608 for specific patching guidance and updated container images.

To verify you are running a patched version, check the container image tag and ensure it is at or above the patched version.

Workarounds

• If immediate patching is not possible, restrict container access to only trusted users and services
• Implement read-only file systems for sensitive directories within containers where feasible
• Use security contexts in Kubernetes to run containers with minimal privileges
• Deploy runtime security tools to detect and block unauthorized file modifications

# Verify kubernetes-nmstate-handler container version
kubectl get pods -n nmstate -o jsonpath='{.items[*].spec.containers[*].image}' | grep kubernetes-nmstate-handler

# Apply security context to restrict container capabilities
# Add to pod specification:
# securityContext:
#   readOnlyRootFilesystem: true
#   runAsNonRoot: true
#   allowPrivilegeEscalation: false