Potential Persistence Via DLLPathOverride

Hunt Hypothesis

Detects when an attacker adds a new “DLLPathOverride” value to the “Natural Language” key in order to achieve persistence which will get invoked by “SearchIndexer.exe” process

Detection Rule

Sigma (Original)

title: Potential Persistence Via DLLPathOverride
id: a1b1fd53-9c4a-444c-bae0-34a330fc7aa8
status: test
description: Detects when an attacker adds a new "DLLPathOverride" value to the "Natural Language" key in order to achieve persistence which will get invoked by "SearchIndexer.exe" process
references:
    - https://persistence-info.github.io/Data/naturallanguage6.html
    - https://www.hexacorn.com/blog/2018/12/30/beyond-good-ol-run-key-part-98/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-07-21
modified: 2023-08-17
tags:
    - attack.persistence
logsource:
    category: registry_set
    product: windows
detection:
    selection_root:
        # The path can be for multiple languages
        # Example:  HKLM\System\CurrentControlSet\Control\ContentIndex\Language\English_UK
        #           HKLM\System\CurrentControlSet\Control\ContentIndex\Language\English_US
        #           HKLM\System\CurrentControlSet\Control\ContentIndex\Language\Neutral
        TargetObject|contains: '\SYSTEM\CurrentControlSet\Control\ContentIndex\Language\'
    selection_values:
        TargetObject|contains:
            - '\StemmerDLLPathOverride'
            - '\WBDLLPathOverride'
            - '\StemmerClass'
            - '\WBreakerClass'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imRegistry
| where RegistryKey endswith "\\SYSTEM\\CurrentControlSet\\Control\\ContentIndex\\Language*" and (RegistryKey contains "\\StemmerDLLPathOverride" or RegistryKey contains "\\WBDLLPathOverride" or RegistryKey contains "\\StemmerClass" or RegistryKey contains "\\WBreakerClass")

KQL (Microsoft 365 Defender)

DeviceRegistryEvents
| where RegistryKey endswith "\\SYSTEM\\CurrentControlSet\\Control\\ContentIndex\\Language*" and (RegistryKey contains "\\StemmerDLLPathOverride" or RegistryKey contains "\\WBDLLPathOverride" or RegistryKey contains "\\StemmerClass" or RegistryKey contains "\\WBreakerClass")

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Persistence

References

• https://persistence-info.github.io/Data/naturallanguage6.html
• https://www.hexacorn.com/blog/2018/12/30/beyond-good-ol-run-key-part-98/
• SigmaHQ Rule