Invoke-Obfuscation Via Use Rundll32 - Security

Severity: high
Author: Nikita Nazarov, oscd.community
Source: upstream

Detects Obfuscated Powershell via use Rundll32 in Scripts

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Defense Evasion	`T1027` Obfuscated Files or Information

Event coverage

Provider	Event ID	Title
Security-Auditing	4697	A service was installed in the system.

Stages and Predicates

Stage 1: `selection`

or:
ServiceFileName|contains: comspec
ServiceFileName|contains: iex
ServiceFileName|contains: invoke
ServiceFileName|contains: value
ServiceFileName|contains: '&&'
ServiceFileName|contains: rundll32
ServiceFileName|contains: shell32.dll
ServiceFileName|contains: shellexec_rundll

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
`ServiceFileName`	match	`&&` corpus 3 (sigma 3) `comspec` `iex` `invoke` corpus 2 (sigma 2) `rundll32` corpus 2 (sigma 2) `shell32.dll` corpus 2 (sigma 2) `shellexec_rundll` corpus 2 (sigma 2) `value`

Neighbors

Broader alternatives (more inclusive than this rule)

These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.

CobaltStrike Service Installations - Security [sigma] (drops 5 filters this rule applies) (first-stage match only; downstream stages may differ)
Invoke-Obfuscation Obfuscated IEX Invocation - Security [sigma] (drops 5 filters this rule applies) (first-stage match only; downstream stages may differ)
Meterpreter or Cobalt Strike Getsystem Service Installation - Security [sigma] (drops 5 filters this rule applies) (first-stage match only; downstream stages may differ)
Service Installed By Unusual Client - Security [sigma] (drops 5 filters this rule applies) (first-stage match only; downstream stages may differ)