NET NGenAssemblyUsageLog Registry Key Tamper

Hunt Hypothesis

Detects changes to the NGenAssemblyUsageLog registry key. .NET Usage Log output location can be controlled by setting the NGenAssemblyUsageLog CLR configuration knob in the Registry or by configuring

Detection Rule

Sigma (Original)

title: NET NGenAssemblyUsageLog Registry Key Tamper
id: 28036918-04d3-423d-91c0-55ecf99fb892
status: test
description: |
  Detects changes to the NGenAssemblyUsageLog registry key.
  .NET Usage Log output location can be controlled by setting the NGenAssemblyUsageLog CLR configuration knob in the Registry or by configuring an environment variable (as described in the next section).
  By simplify specifying an arbitrary value (e.g. fake output location or junk data) for the expected value, a Usage Log file for the .NET execution context will not be created.
references:
    - https://bohops.com/2021/03/16/investigating-net-clr-usage-log-tampering-techniques-for-edr-evasion/
author: frack113
date: 2022-11-18
modified: 2023-08-17
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1112
logsource:
    product: windows
    category: registry_set
detection:
    selection:
        TargetObject|endswith: 'SOFTWARE\Microsoft\.NETFramework\NGenAssemblyUsageLog'
    condition: selection
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imRegistry
| where RegistryKey endswith "SOFTWARE\\Microsoft\\.NETFramework\\NGenAssemblyUsageLog"

KQL (Microsoft 365 Defender)

DeviceRegistryEvents
| where RegistryKey endswith "SOFTWARE\\Microsoft\\.NETFramework\\NGenAssemblyUsageLog"

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Persistence
• Technique: T1112 — T1112

References

• https://bohops.com/2021/03/16/investigating-net-clr-usage-log-tampering-techniques-for-edr-evasion/
• SigmaHQ Rule