Detection rules › Sigma

Potential DLL Sideloading Of MsCorSvc.DLL

Status
test
Severity
medium
Log source
category image_load, product windows
Author
Wietze Beukema
Source
github.com/SigmaHQ/sigma

Detects potential DLL sideloading of "mscorsvc.dll".

Known false positives

  • Legitimate applications loading their own versions of the DLL mentioned in this rule.

MITRE ATT&CK coverage

Telemetry coverage

ProviderRecord / event type
SysmonEvent ID 7: Image loaded

Rule body

title: Potential DLL Sideloading Of MsCorSvc.DLL
id: cdb15e19-c2d0-432a-928e-e49c8c60dcf2
status: test
description: Detects potential DLL sideloading of "mscorsvc.dll".
references:
    - https://hijacklibs.net/entries/microsoft/built-in/mscorsvc.html
author: Wietze Beukema
date: 2024-07-11
modified: 2025-02-26
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.execution
    - attack.stealth
    - attack.t1574.001
logsource:
    product: windows
    category: image_load
detection:
    selection:
        ImageLoaded|endswith: '\mscorsvc.dll'
    filter_main_generic:
        ImageLoaded|startswith:
            - 'C:\Windows\Microsoft.NET\Framework\'
            - 'C:\Windows\Microsoft.NET\Framework64\'
            - 'C:\Windows\Microsoft.NET\FrameworkArm\'
            - 'C:\Windows\Microsoft.NET\FrameworkArm64\'
            - 'C:\Windows\WinSxS\'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Legitimate applications loading their own versions of the DLL mentioned in this rule.
level: medium

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_main_*

Stage 1: selection

selection:
    ImageLoaded|endswith: '\mscorsvc.dll'

Stage 2: not filter_main_generic

filter_main_generic:
    ImageLoaded|startswith:
        - 'C:\Windows\Microsoft.NET\Framework\'
        - 'C:\Windows\Microsoft.NET\Framework64\'
        - 'C:\Windows\Microsoft.NET\FrameworkArm\'
        - 'C:\Windows\Microsoft.NET\FrameworkArm64\'
        - 'C:\Windows\WinSxS\'

Exclusions

The rule actively suppresses these predicates.

FieldKindExcluded valuesSearch
ImageLoadedstarts_withC:\Windows\Microsoft.NET\Framework64\excludes:ImageLoaded field:"ImageLoaded" value:"C:\Windows\Microsoft.NET\Framework64\"
ImageLoadedstarts_withC:\Windows\Microsoft.NET\FrameworkArm64\excludes:ImageLoaded field:"ImageLoaded" value:"C:\Windows\Microsoft.NET\FrameworkArm64\"
ImageLoadedstarts_withC:\Windows\Microsoft.NET\FrameworkArm\excludes:ImageLoaded field:"ImageLoaded" value:"C:\Windows\Microsoft.NET\FrameworkArm\"
ImageLoadedstarts_withC:\Windows\Microsoft.NET\Framework\excludes:ImageLoaded field:"ImageLoaded" value:"C:\Windows\Microsoft.NET\Framework\"
ImageLoadedstarts_withC:\Windows\WinSxS\excludes:ImageLoaded field:"ImageLoaded" value:"C:\Windows\WinSxS\"

Indicators

These rows show field, operator, and value matches.