Suspicious Screensaver Binary File Creation

Status: test
Severity: medium
Log source: category file_event, product windows
Author: frack113
Source: github.com/SigmaHQ/sigma

Adversaries may establish persistence by executing malicious content triggered by user inactivity. Screensavers are programs that execute after a configurable time of user inactivity and consist of Portable Executable (PE) files with a .scr file extension

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1546.002` Event Triggered Execution: Screensaver
Privilege Escalation	`T1546.002` Event Triggered Execution: Screensaver

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 11: FileCreate

Rule body

title: Suspicious Screensaver Binary File Creation
id: 97aa2e88-555c-450d-85a6-229bcd87efb8
status: test
description: |
    Adversaries may establish persistence by executing malicious content triggered by user inactivity.
    Screensavers are programs that execute after a configurable time of user inactivity and consist of Portable Executable (PE) files with a .scr file extension
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1546.002/T1546.002.md
author: frack113
date: 2021-12-29
modified: 2022-11-08
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1546.002
logsource:
    product: windows
    category: file_event
detection:
    selection:
        TargetFilename|endswith: '.scr'
    filter_generic:
        Image|endswith:
            - '\Kindle.exe'
            - '\Bin\ccSvcHst.exe' # Symantec Endpoint Protection
    filter_tiworker:
        # ParentCommandLine: C:\WINDOWS\system32\svchost.exe -k DcomLaunch -p
        Image|endswith: '\TiWorker.exe'
        TargetFilename|endswith: '\uwfservicingscr.scr'
    condition: selection and not 1 of filter_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_*

Stage 1: `selection`

selection:
    TargetFilename|endswith: '.scr'

Stage 2: `not filter_*`

filter_generic:
    Image|endswith:
        - '\Kindle.exe'
        - '\Bin\ccSvcHst.exe'
filter_tiworker:
    Image|endswith: '\TiWorker.exe'
    TargetFilename|endswith: '\uwfservicingscr.scr'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	ends_with	`\TiWorker.exe`	`excludes:Image` `field:"Image" value:"\TiWorker.exe"`
`TargetFilename`	ends_with	`\uwfservicingscr.scr`	`excludes:TargetFilename` `field:"TargetFilename" value:"\uwfservicingscr.scr"`
`Image`	ends_with	`\Bin\ccSvcHst.exe`	`excludes:Image` `field:"Image" value:"\Bin\ccSvcHst.exe"`
`Image`	ends_with	`\Kindle.exe`	`excludes:Image` `field:"Image" value:"\Kindle.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`TargetFilename`	ends_with	`.scr` corpus 8 (sigma 8)	`field:"TargetFilename" kind:ends_with value:".scr"`