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Detection rules › Kusto

VMware ESXi - Unexpected disk image

Status
available
Severity
medium
Time window
14d
Group by
DstHostname
Source
github.com/Azure/Azure-Sentinel

'Detects unexpected disk image for VM.'

MITRE ATT&CK coverage

TacticTechniques
ImpactT1496 Resource Hijacking

Rule body kusto

id: 395c5560-ddc2-45b2-aafe-2e3f64528d3d
name: VMware ESXi - Unexpected disk image
description: |
  'Detects unexpected disk image for VM.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: SyslogAma
    datatypes:
      - Syslog
queryFrequency: 1h
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Impact
relevantTechniques:
  - T1496
query: |
  let img_ =
  VMwareESXi
  | where SyslogMessage has ('Matched discovered VM')
  | extend DstHostname = extract(@'vim.VirtualMachine\S+,(.*?)\]', 1, SyslogMessage)
  | extend kImageName = extract(@'ds:///vmfs/volumes/(.*)/(.*?),', 2, SyslogMessage)
  | summarize img_lst = makeset(kImageName) by DstHostname;
  VMwareESXi
  | where SyslogMessage has ('Matched discovered VM')
  | extend DstHostname = extract(@'vim.VirtualMachine\S+,(.*?)\]', 1, SyslogMessage)
  | extend ImageName = extract(@'ds:///vmfs/volumes/(.*)/(.*?),', 2, SyslogMessage)
  | join (img_) on DstHostname
  | where img_lst !has ImageName
  | extend HostCustomEntity = DstHostname
entityMappings:
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: HostCustomEntity
version: 1.0.2
kind: Scheduled

Stages and Predicates

Let binding: img_

let img_ = VMwareESXi
| where SyslogMessage has ('Matched discovered VM')
| extend DstHostname = extract(@'vim.VirtualMachine\S+,(.*?)\]', 1, SyslogMessage)
| extend kImageName = extract(@'ds:///vmfs/volumes/(.*)/(.*?),', 2, SyslogMessage)
| summarize img_lst = makeset(kImageName) by DstHostname;

Stage 1: source

VMwareESXi

Stage 2: where

| where SyslogMessage has ('Matched discovered VM')

Stage 3: extend

| extend DstHostname = extract(@'vim.VirtualMachine\S+,(.*?)\]', 1, SyslogMessage)

Stage 4: extend

| extend ImageName = extract(@'ds:///vmfs/volumes/(.*)/(.*?),', 2, SyslogMessage)

Stage 5: join

| join (img_) on DstHostname

Stage 6: where

| where img_lst !has ImageName

Stage 7: extend

| extend HostCustomEntity = DstHostname

Stage 8: summarize

summarize by DstHostname

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
img_lstmatchImageName

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
SyslogMessagematch
  • Matched discovered VM transforms: term

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

FieldSource
DstHostnamesummarize