What Is a Host Operating System (OS)?

Host OS security involves many aspects — scanning for vulnerabilities, hardening the system based on industry benchmarks (such as NIST, SANS, or CIS), and safeguarding against improper access control (e.g., Docker commands, SSH commands, sudo commands) or file tampering. Both Linux and Windows-based OS are commonly used and supported by most orchestration vendors, depending on the application.

When deploying on private infrastructure, ensure compliance with the minimum hardware requirements and choose a compatible OS, such as Linux or Windows, supported by your orchestration vendor.

By prioritizing host OS security, you can establish a strong foundation for your container environment, protecting your applications and maintaining overall system integrity.

Implement Industry-Standard Security Benchmarks

To ensure a consistent and secure host OS configuration, adhere to industry-standard security benchmarks. The Center for Internet Security (CIS) provides comprehensive benchmarks for various host OS options. These benchmarks offer configuration guidelines for system settings, security controls, and validation and testing procedures. Following these recommendations will help maintain a secure host OS while running container workloads.

Customizing OS Configurations for Improved Security

Hardening the host OS for container environments involves several steps. Start by disabling unnecessary services to reduce the attack surface and minimize resource usage. Close unused network ports to prevent unauthorized access, and remove unneeded applications and packages to reduce potential vulnerabilities. Restrict the use of insecure protocols and enable secure alternatives, such as using SSH over Telnet or HTTPS over HTTP. Finally, enable and configure security features like SELinux, AppArmor, or cgroups to enforce access controls and resource isolation. Regularly review system configurations and remove unused software packages to maintain a secure and up-to-date environment.

Container Escape

To understand potential host OS security threats, let’s look at container escape, a security event where malicious actors can leverage a containerized application's vulnerabilities to breach its isolation boundary from the OS and gain access to the host system's resources and other containers.

In general, virtualized hardware isolation provides a stronger security boundary than namespace isolation. The risk of an attacker escaping a container (process) is much higher than escaping a VM due to the weaker isolation created by namespace and cgroup.

Linux implements namespace and cgroup by associating new property fields with each process. These fields, found in the /proc file system, inform the host OS about process visibility and the CPU/memory resources the process can use. From the host OS perspective, a container process appears just like any other process on the host.

Traditional containers, such as Docker or LXC, aren't usually considered sandboxed containers sharing the same host and kernel. Consequently, container escape vulnerabilities can arise. Exploits of container runtime code, like runC (CVE-2019-5736), exemplify such escapes via newly discovered vulnerabilities.

In addition to software vulnerability attack vectors, misconfigurations, such as deploying a container with excessive privileges or critical mount points, can lead to container escape. Container breakout has been a long-standing concern for security teams. Risks can be mitigated, though, by following best practices, such as the Center for Internet Security's (CIS) benchmarks for Docker and Kubernetes (refer to sections 4.1 and 1.7.2, respectively).

Given these exploitable vulnerabilities, it's crucial to understand the risks when deploying containers in a multitenant cluster or having containers with sensitive data co-locate with other untrusted containers.

System-Level Security Features

Implementing system-level security features protects both the host OS and the containers running on it. One key aspect is process isolation. Linux namespaces offer a powerful mechanism for isolating container processes and resources, including process IDs (PIDs), network interfaces, inter-process communication (IPC), hostnames, file system mount points, and user IDs. By leveraging namespaces, containers can run in isolated environments with minimal impact on each other and the host OS.

In addition to namespaces, Seccomp profiles, a Linux kernel feature, contribute to the overall security of the container environment by restricting the system calls that a container can execute. Seccomp profiles provide a way to define a whitelist or blacklist of system calls, reducing the potential attack surface.

Role of SELinux, AppArmor, and cgroups in Host OS Security

SELinux (Security-Enhanced Linux), AppArmor, and cgroups play essential roles in securing the host OS for containers. SELinux enforces mandatory access controls (MAC) by restricting processes and users based on predefined security policies. AppArmor, similar to SELinux, confines applications to a limited set of resources and permissions, isolating them from the rest of the system.

Control groups (cgroups) are a Linux kernel feature that allows the limitation and prioritization of resources — such as CPU time, system memory, network bandwidth, or combinations of these resources — for a set of processes. In containerization technologies, they’re essential for efficient resource utilization and ensuring that containers run in isolation and don't monopolize system resources, which helps maintain overall system stability and security (by preventing resource exhaustion attacks).

By setting limits on CPU, memory, I/O, and other resources, administrators can ensure that container workloads don’t consume excessive resources, potentially impacting other containers or the host OS.

Enabling and Configuring Mandatory Access Controls (MAC)

Mandatory access controls (MAC) are essential for securing container environments, as they enforce strict security policies that prevent unauthorized access and resource usage. To enable and configure MAC, follow these steps:

• Choose a MAC system like SELinux or AppArmor, based on the host OS and compatibility with container runtimes and orchestration tools.
• Configure the MAC system according to the security requirements and policies of your organization, including defining security labels, profiles, and permissions.
• Test the MAC configuration to ensure it effectively restricts access and resource usage according to the defined policies.

Implementing Strong User Authentication and Access Controls

Strong user authentication and access controls help secure the host OS. Implement SSH key-based authentication to replace less secure password-based authentication, reducing the risk of unauthorized access. Additionally, consider enabling two-factor authentication (2FA) to add an extra layer of security.

To manage user access, establish a role-based access control (RBAC) system that defines roles and permissions based on the principle of least privilege. Assign users to roles that grant them the minimum level of access necessary to perform their tasks.

Patch Management and Vulnerability Management

Maintaining up-to-date software is a fundamental aspect of container security. Effective patch management and vulnerability management processes are necessary to ensure that the host OS, container images, and application dependencies remain secure.

Automating patch management and security compliance checks

Automation is key to maintaining a secure and compliant host OS. Implement automated patch management tools that monitor, download, and install updates according to predefined schedules and policies. Additionally, use automated security compliance checks to validate the host OS's adherence to security benchmarks and organizational policies.

To achieve effective patch management, automation is key. Implement automated patch management tools such as Ansible, Puppet, or Chef that monitor, download, and install updates according to predefined schedules and policies. Regularly updating the host OS, container images, and application dependencies helps to address security vulnerabilities and maintain a secure environment.

Monitoring and Managing Software Vulnerabilities in the Host OS

Vulnerability management involves several steps, including scanning, prioritizing, remediating, and validating fixes. Integrating vulnerability scanning tools, such as OpenSCAP or Trivy, into the CI/CD pipeline allows for early detection of vulnerabilities in container images and application dependencies. By establishing a vulnerability management process, organizations can ensure that security issues are addressed in a timely and effective manner, minimizing the risk of exploitation.

File System and Storage Security

Securing the file system and storage used by containers is critical for preventing unauthorized data access and tampering. To achieve this, mount the host file system with options such as "nodev," "nosuid," and "noexec" to prevent device access, setuid execution, and executable file execution, respectively. Implement granular access controls on the host file system and container volumes using Linux Security Modules (LSMs) and Access Control Lists (ACLs) and assign permissions according to the least privileged principle. This approach minimizes the risk of unauthorized access or tampering.

For container storage, it’s crucial to protect data at rest and in transit. Implement encrypted file systems, such as dm-crypt or eCryptfs, to secure data at rest. Additionally, use encrypted communication channels like Transport Layer Security (TLS) to protect data in transit from unauthorized access or interception.

When using external storage solutions, such as cloud-based storage services, ensure that proper security measures are in place, including encryption and access controls. Regularly review and update security configurations for external storage to maintain a secure environment.

Monitoring and Auditing File Access and Changes Within the Host OS

Continuous monitoring and auditing of file access and changes within the host OS help detect potential security incidents and maintain compliance. Employ file integrity monitoring (FIM) tools to track modifications to critical files and directories. Configure alerts to notify security teams of unusual activity. Implement audit logging to record file access events and integrate them with security information and event management (SIEM) solutions for analysis and correlation with other security events.

Host-Level Firewall Configuration and Security

Configuring and securing the host-level firewall is essential for protecting both the host OS and the containers running on it from network-based attacks. Implementing a default deny-all policy ensures that only necessary traffic is allowed, reducing the risk of unauthorized access. To achieve this, set the default INPUT, FORWARD, and OUTPUT chains to DROP in iptables or nftables, and create allow rules for specific ports, protocols, and IP addresses as needed.

Administrators can ensure that containers operate in segregated network environments by creating network namespaces and assigning containers to separate namespaces based on their purpose and trust levels. This will restrict container access to the host network, further enhancing security.

Logging, Monitoring, and Auditing

To maintain the security of the host OS and containers, implement centralized logging and monitoring. Collect logs from the host OS, container runtime, orchestration tools, and applications to facilitate incident detection and response and identify potential security issues.

Configure syslog or journald on the host OS to collect and store logs from various sources. Use log aggregation and analysis tools, such as Elasticsearch, Fluentd, Kibana, or Prisma Cloud to consolidate and analyze logs from multiple sources. Integrate log analysis with SIEM solutions, threat intelligence feeds, and incident response processes to enhance the detection and remediation of security incidents.

Container Performance Monitoring

Monitoring container performance metrics, such as CPU usage, memory consumption, and network activity, helps identify abnormal behavior or signs of compromise. Use tools like Prometheus, Grafana, or cAdvisor to monitor container performance metrics and configure alerts for anomalous behavior.

Auditing and Compliance

Auditing is essential for ensuring ongoing compliance with security best practices and regulatory requirements. Regularly audit the host OS, container configurations, and application dependencies to identify potential security issues or areas for improvement. Use tools such as Docker Bench, Kubernetes CIS Benchmark, or Clair to audit and validate container configurations.

Tracking Container-Related Activities

Configure audit rules using the Linux audit system or other auditing tools to track container-related activities on the host OS, such as container creation, deletion, and network activity. Regularly review audit logs to identify suspicious behavior and potential security incidents. By implementing effective logging, monitoring, and auditing processes, organizations can maintain a secure container environment and respond quickly to security incidents.

Host OS Security FAQs