ShimCache Flush

Hunt Hypothesis

Detects actions that clear the local ShimCache and remove forensic evidence

Detection Rule

Sigma (Original)

title: ShimCache Flush
id: b0524451-19af-4efa-a46f-562a977f792e
status: stable
description: Detects actions that clear the local ShimCache and remove forensic evidence
references:
    - https://medium.com/@blueteamops/shimcache-flush-89daff28d15e
author: Florian Roth (Nextron Systems)
date: 2021-02-01
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1112
logsource:
    category: process_creation
    product: windows
detection:
    selection1a:
        CommandLine|contains|all:
            - 'rundll32'
            - 'apphelp.dll'
    selection1b:
        CommandLine|contains:
            - 'ShimFlushCache'
            - '#250'
    selection2a:
        CommandLine|contains|all:
            - 'rundll32'
            - 'kernel32.dll'
    selection2b:
        CommandLine|contains:
            - 'BaseFlushAppcompatCache'
            - '#46'
    condition: ( selection1a and selection1b ) or ( selection2a and selection2b )
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imProcessCreate
| where ((TargetProcessCommandLine contains "rundll32" and TargetProcessCommandLine contains "apphelp.dll") and (TargetProcessCommandLine contains "ShimFlushCache" or TargetProcessCommandLine contains "#250")) or ((TargetProcessCommandLine contains "rundll32" and TargetProcessCommandLine contains "kernel32.dll") and (TargetProcessCommandLine contains "BaseFlushAppcompatCache" or TargetProcessCommandLine contains "#46"))

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Persistence
• Technique: T1112 — T1112

References

• https://medium.com/@blueteamops/shimcache-flush-89daff28d15e
• SigmaHQ Rule