Images, patching and privilege

Source: Azure Compute Standards, sys_kb_id=937eb90b3b650f107f43b50236e45a16.

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Global rules

1. Monthly patch cycle.
2. Scan vendor images before entry.
3. Images and base layers must NOT run as privileged.

Rule 3 applies to container base layers as well as VM images. In Kubernetes terms: securityContext.privileged: true is a violation, and it compounds with the AKS rules on CAP_SYS_ADMIN and read-only root filesystems.

Image approval

Image type	Requirement
Microsoft marketplace, unmodified	Qualifies as security-approved automatically
Microsoft marketplace, modified	Becomes a custom image — see below
Custom image	Periodic security review plus monthly patch and recapture
Any vendor image	Scanned before entry

Note

“Recapture” means the image is rebuilt and re-published monthly, not merely patched in place on running instances.

Container base images

Warning

[TBD: the standards do not enumerate an approved container base image or registry list. The Compute standard's image rules are written for VM images and the marketplace; the CI/CD standard requires "approved base images" without defining the list.]

The plugin’s PreToolUse hook enforces an allowlist at hooks/approved-base-images.txt, which currently contains only:

Entry	Why
mcr.microsoft.com/	The narrowest reading of “unmodified Microsoft images qualify”
scratch	An empty base layer
commented placeholders	For the internal registry, once it is confirmed

Confirm the real list with Infra CloudOps and AppSec, then edit that file. Until then, the hook will block common public images such as node:24. The off-switch is PATTERSON_ENGINEERING_HOOKS=off.

Scanning

Container scanning uses Trivy or Checkmarx (CI/CD Pipeline Standards). Trivy is approved with no approval needed; the Approved Software standard notes “Checkmarx will replace this tool”. Vulnerability scanning across the estate is Qualys, running nightly and creating ServiceNow tickets (Monitoring & Alerting standard).

[TBD: the standard does not state a severity threshold that blocks an image from entry.]

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Source of truth: plugins/patterson-engineering/skills/azure-compute-standards/references/images-and-patching.md in the patterson-corp repository.