CHAIN-117 — VMSS without OS auto-upgrade + public SSH

Summary

Severity: High · Likelihood: Medium · Logic: ALL

Why this chain matters

A VM Scale Set has OS auto-upgrade disabled and its instance count exposes SSH to the internet. Instances run months-old kernels; any published CVE with public exploit gives one-click RCE on every instance in the pool.

Component rules

This chain fires when its trigger conditions are met by the following rules. Click any rule to see its detection logic and compliance mappings.

Rule ID	Role
zt_wl_029	Trigger
zt_net_001	Trigger

Attack walkthrough

Step 1 — Match VMSS banner to known kernel CVE.

Actor: Attacker
MITRE ATT&CK: T1595
Enabled by: zt_wl_029

Attacker gain: Exploit candidate.

Step 2 — Exploit kernel CVE; root shell on all instances.

Actor: Attacker
MITRE ATT&CK: T1210
Enabled by: zt_net_001

Attacker gain: Fleet-wide compromise.

Blast radius

Initial access	Internet SSH + unpatched kernel.
Max privilege	Root on every VMSS instance.
Data at risk	Workload data, MI tokens
Services at risk	VMSS, Dependent services

How the logic works

The chain fires only when every rule above has at least one finding in the current scan. Missing any one rule breaks the chain — so remediating any single step disrupts the attack path.