Potential Persistence Via New AMSI Providers - Registry

Hunt Hypothesis

Detects when an attacker adds a new AMSI provider via the Windows Registry to bypass AMSI (Antimalware Scan Interface) protections. Attackers may add custom AMSI providers to persist on the system and

Detection Rule

Sigma (Original)

title: Potential Persistence Via New AMSI Providers - Registry
id: 33efc23c-6ea2-4503-8cfe-bdf82ce8f705
status: test
description: |
    Detects when an attacker adds a new AMSI provider via the Windows Registry to bypass AMSI (Antimalware Scan Interface) protections.
    Attackers may add custom AMSI providers to persist on the system and evade detection by security software that relies on AMSI for scanning scripts and other content.
    This technique is often used in conjunction with fileless malware and script-based attacks to maintain persistence while avoiding detection.
references:
    - https://persistence-info.github.io/Data/amsi.html
    - https://github.com/gtworek/PSBits/blob/8d767892f3b17eefa4d0668f5d2df78e844f01d8/FakeAMSI/FakeAMSI.c
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-07-21
modified: 2025-10-26
tags:
    - attack.persistence
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|contains:
            - '\SOFTWARE\Microsoft\AMSI\Providers\'
            - '\SOFTWARE\WOW6432Node\Microsoft\AMSI\Providers\'
    filter_optional_avast:
        Image:
            - 'C:\Program Files\Avast Software\Avast\RegSvr.exe'
            - 'C:\Program Files\Avast Software\Avast\x86\RegSvr.exe'
        TargetObject|contains: '\{FB904E4E-D2C7-4C8D-8492-B620BB9896B1}'
    filter_optional_avg:
        Image:
            - 'C:\Program Files\AVG\Antivirus\RegSvr.exe'
            - 'C:\Program Files\AVG\Antivirus\x86\RegSvr.exe'
        TargetObject|contains: '\{FB904E4E-D2C7-4C8D-8492-B620BB9896B1}'
    filter_optional_avira:
        Image: 'C:\Program Files\Avira\Endpoint Protection SDK\endpointprotection.exe'
        TargetObject|contains: '\{00000001-3DCC-4B48-A82E-E2071FE58E05}'
    condition: selection and not 1 of filter_optional_*
falsepositives:
    - Legitimate security products adding their own AMSI providers. Filter these according to your environment.
level: medium
regression_tests_path: regression_data/rules/windows/registry/registry_set/registry_set_persistence_amsi_providers/info.yml

KQL (Azure Sentinel)

imRegistry
| where (RegistryKey endswith "\\SOFTWARE\\Microsoft\\AMSI\\Providers*" or RegistryKey endswith "\\SOFTWARE\\WOW6432Node\\Microsoft\\AMSI\\Providers*") and (not((((ActingProcessName in~ ("C:\\Program Files\\Avast Software\\Avast\\RegSvr.exe", "C:\\Program Files\\Avast Software\\Avast\\x86\\RegSvr.exe")) and RegistryKey contains "\\{FB904E4E-D2C7-4C8D-8492-B620BB9896B1}") or ((ActingProcessName in~ ("C:\\Program Files\\AVG\\Antivirus\\RegSvr.exe", "C:\\Program Files\\AVG\\Antivirus\\x86\\RegSvr.exe")) and RegistryKey contains "\\{FB904E4E-D2C7-4C8D-8492-B620BB9896B1}") or (ActingProcessName =~ "C:\\Program Files\\Avira\\Endpoint Protection SDK\\endpointprotection.exe" and RegistryKey contains "\\{00000001-3DCC-4B48-A82E-E2071FE58E05}"))))

Required Data Sources

False Positive Guidance

• Legitimate security products adding their own AMSI providers. Filter these according to your environment.

MITRE ATT&CK Context

• Tactic: Persistence

References

• https://persistence-info.github.io/Data/amsi.html
• https://github.com/gtworek/PSBits/blob/8d767892f3b17eefa4d0668f5d2df78e844f01d8/FakeAMSI/FakeAMSI.c
• SigmaHQ Rule