scc-security

OpenShift Security Context Constraints (SCC)

SCCs control what actions pods can perform and what host resources they can access. If no security context is specified, OpenShift applies the restricted SCC by default.

What SCCs Control

• Privileged container execution
• Linux capabilities requested by containers
• Host directory volume mounts
• SELinux context
• Container user and group IDs
• Host namespace and networking access
• FSGroup ownership of volumes
• Supplemental groups
• Read-only root filesystem requirement
• Volume types
• Seccomp profiles

SCC Reference

SCC	Description	When to Use
restricted	Denies all host features; requires namespace-allocated UID and SELinux label. Most restrictive.	Default for all workloads; prefer this unless a specific relaxation is justified
nonroot	Like restricted, but allows any non-root UID	When the container must run as a specific non-root UID
anyuid	Like restricted, but allows any UID/GID	When the container requires a specific UID (including root UID without root privileges)
hostnetwork	Allows host networking and ports; requires namespace UID/SELinux	Only for pods that must bind to host network interfaces
hostaccess	Allows all host namespaces; requires namespace UID/SELinux	Only for trusted pods requiring host namespace access
hostmount-anyuid	Like restricted, but allows host mounts and any UID	Only for pods requiring host filesystem access (e.g., persistent volume recycler)
privileged	Full access to all host features; any user, group, SELinux context	Only for cluster administration requiring maximum access
node-exporter	Purpose-built for the Prometheus node exporter	Only for the node exporter DaemonSet
custom	Administrator-defined constraints	Requires careful security review; document every relaxation

Security Review Guidelines

• Start from restricted and relax only when a specific capability is justified
• Document why a workload cannot run under restricted
• Custom SCCs require particular scrutiny: every relaxation from restricted must have a documented rationale
• Review that SCCs are bound to the correct ServiceAccounts, not overly broad groups
• Verify that no workload uses privileged SCC unless it is a cluster administration component
• Check that runAsNonRoot: true is set where possible
• Check that readOnlyRootFilesystem: true is set where possible

Implementation Checklist

• All workloads use restricted SCC unless a specific exception is documented
• No workload uses privileged SCC without cluster-admin justification
• Custom SCCs document every relaxation from restricted
• SCC bindings target specific ServiceAccounts, not broad groups
• runAsNonRoot: true is set in the pod security context
• readOnlyRootFilesystem: true is set in container security contexts
• Host path mounts are justified and documented
• Host networking is only enabled for pods that require it

References

• Managing Security Context Constraints
• Runtime Privilege and Linux Capabilities