WMI Backdoor Exchange Transport Agent

Severity: critical
Author: Florian Roth (Nextron Systems)
Source: upstream

Detects a WMI backdoor in Exchange Transport Agents via WMI event filters

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1546.003` Event Triggered Execution: Windows Management Instrumentation Event Subscription
Privilege Escalation	`T1546.003` Event Triggered Execution: Windows Management Instrumentation Event Subscription

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `selection`

ParentImage|endswith: '\EdgeTransport.exe'

Stage 2: `not 1 of filter_*`

or:
Image|endswith: '\Bin\OleConverter.exe'
Image|startswith: 'C:\Program Files\Microsoft\Exchange Server\'
Image: 'C:\Windows\System32\conhost.exe'

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.

Field	Kind	Values
`Image`	ends_with	`\Bin\OleConverter.exe`
`Image`	eq	`C:\Windows\System32\conhost.exe` corpus 2 (sigma 2)
`Image`	starts_with	`C:\Program Files\Microsoft\Exchange Server\` corpus 3 (sigma 3)
`ParentImage`	ends_with	`\EdgeTransport.exe`