ScreenSaver Registry Key Set

Severity: medium
Author: Jose Luis Sanchez Martinez (@Joseliyo_Jstnk)
Source: upstream

Detects registry key established after masqueraded .scr file execution using Rundll32 through desk.cpl

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.011` System Binary Proxy Execution: Rundll32

Event coverage

Provider	Event ID	Title
Sysmon	13	RegistryEvent (Value Set)

Stages and Predicates

Stage 1: `selection`

Image|endswith: '\rundll32.exe'

Stage 2: `registry`

Details|endswith: .scr
TargetObject|contains: '\Control Panel\Desktop\SCRNSAVE.EXE'

Stage 3: `not filter`

or:
Details|contains: 'C:\Windows\SysWOW64\'
Details|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
`Details`	ends_with	`.scr`
`Details`	match	`C:\Windows\SysWOW64\` `C:\Windows\System32\`
`Image`	ends_with	`\rundll32.exe` corpus 76 (sigma 76)
`TargetObject`	match	`\Control Panel\Desktop\SCRNSAVE.EXE`