Potential DLL Sideloading Using Coregen.exe

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

Detect usage of the "coregen.exe" (Microsoft CoreCLR Native Image Generator) binary to sideload arbitrary DLLs.

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1055` Process Injection
Stealth	`T1055` Process Injection `T1218` System Binary Proxy Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 7: Image loaded

Rule body

title: Potential DLL Sideloading Using Coregen.exe
id: 0fa66f66-e3f6-4a9c-93f8-4f2610b00171
status: test
description: Detect usage of the "coregen.exe" (Microsoft CoreCLR Native Image Generator) binary to sideload arbitrary DLLs.
references:
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Coregen/
author: frack113
date: 2022-12-31
tags:
    - attack.privilege-escalation
    - attack.stealth
    - attack.t1218
    - attack.t1055
logsource:
    category: image_load
    product: windows
detection:
    selection:
        Image|endswith: '\coregen.exe'
    filter_main_legit_paths:
        ImageLoaded|startswith:
            - 'C:\Program Files (x86)\Microsoft Silverlight\'
            - 'C:\Program Files\Microsoft Silverlight\'
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    Image|endswith: '\coregen.exe'

Stage 2: `not filter_main_legit_paths`

filter_main_legit_paths:
    ImageLoaded|startswith:
        - 'C:\Program Files (x86)\Microsoft Silverlight\'
        - 'C:\Program Files\Microsoft Silverlight\'
        - 'C:\Windows\System32\'
        - 'C:\Windows\SysWOW64\'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`ImageLoaded`	starts_with	`C:\Program Files (x86)\Microsoft Silverlight\`	`excludes:ImageLoaded` `field:"ImageLoaded" value:"C:\Program Files (x86)\Microsoft Silverlight\"`
`ImageLoaded`	starts_with	`C:\Program Files\Microsoft Silverlight\`	`excludes:ImageLoaded` `field:"ImageLoaded" value:"C:\Program Files\Microsoft Silverlight\"`
`ImageLoaded`	starts_with	`C:\Windows\SysWOW64\`	`excludes:ImageLoaded` `field:"ImageLoaded" value:"C:\Windows\SysWOW64\"`
`ImageLoaded`	starts_with	`C:\Windows\System32\`	`excludes:ImageLoaded` `field:"ImageLoaded" value:"C:\Windows\System32\"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\coregen.exe`	`field:"Image" kind:ends_with value:"\coregen.exe"`