Potential Obfuscated Ordinal Call Via Rundll32

Severity: medium
Author: Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
Source: upstream

Detects execution of "rundll32" with potential obfuscated ordinal calls

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1027.010` Obfuscated Files or Information: Command Obfuscation

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
CommandLine|contains: rundll32
Image|endswith: '\rundll32.exe'
OriginalFileName: RUNDLL32.EXE

Stage 2: `all of selection_cli`

or:
CommandLine|contains: '#+'
CommandLine|contains: '#-'
CommandLine|contains: '#0'
CommandLine|contains: '#655'
CommandLine|contains: '#656'

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
`CommandLine`	match	`#+` corpus 3 (sigma 3) `#-` corpus 3 (sigma 3) `#0` `#655` `#656` `rundll32` corpus 19 (sigma 19)
`Image`	ends_with	`\rundll32.exe` corpus 76 (sigma 76)
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 28 (sigma 25, splunk 3)