Rundll32 Spawned Via Explorer.EXE

Severity: medium
Author: CD_ROM_
Source: upstream

Detects execution of "rundll32.exe" with a parent process of Explorer.exe. This has been observed by variants of Raspberry Robin, as first reported by Red Canary.

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_parent`

ParentImage|endswith: '\explorer.exe'

Stage 2: `all of selection_img`

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

Stage 3: `not 1 of filter_main_generic`

or:
CommandLine|endswith: ' -localserver 22d8c27b-47a1-48d1-ad08-7da7abd79617'
CommandLine|contains: ' C:\Windows\System32\'

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`	ends_with	`-localserver 22d8c27b-47a1-48d1-ad08-7da7abd79617`
`CommandLine`	match	`C:\Windows\System32\`
`Image`	ends_with	`\rundll32.exe` corpus 76 (sigma 76)
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 28 (sigma 25, splunk 3)
`ParentImage`	ends_with	`\explorer.exe` corpus 11 (sigma 11)