Suspicious Antimalware Scan Interface DLL

Last updated 13 days ago on 2025-08-26
Created 3 years ago on 2023-01-17

About

Identifies the creation of the Antimalware Scan Interface (AMSI) DLL in an unusual location. This may indicate an attempt to bypass AMSI by loading a rogue AMSI module instead of the legit one.
Tags
Domain: EndpointOS: WindowsUse Case: Threat DetectionTactic: Defense EvasionData Source: Elastic EndgameData Source: Elastic DefendData Source: SysmonData Source: SentinelOneData Source: Microsoft Defender for EndpointData Source: CrowdstrikeLanguage: eql
Severity
high
Risk Score
73
MITRE ATT&CK™

Defense Evasion (TA0005)(opens in a new tab or window)

License
Elastic License v2(opens in a new tab or window)

Definition

Rule Type
Event Correlation Rule
Integration Pack
Prebuilt Security Detection Rules
Index Patterns
winlogbeat-*logs-endpoint.events.file-*logs-windows.sysmon_operational-*endgame-*logs-sentinel_one_cloud_funnel.*logs-m365_defender.event-*logs-crowdstrike.fdr*
Related Integrations

windows(opens in a new tab or window)

endpoint(opens in a new tab or window)

sentinel_one_cloud_funnel(opens in a new tab or window)

m365_defender(opens in a new tab or window)

crowdstrike(opens in a new tab or window)

Query
file where host.os.type == "windows" and event.type != "deletion" and file.path != null and
  file.name : ("amsi.dll", "amsi") and 
  event.action != "A process changed a file creation time" and 
  not file.path : (
    "?:\\$SysReset\\CloudImage\\Package_for_RollupFix*\\amsi.dll",
    "?:\\Windows\\system32\\amsi.dll",
    "?:\\Windows\\Syswow64\\amsi.dll",
    "?:\\$WINDOWS.~BT\\*\\amsi.dll",
    "?:\\Windows\\CbsTemp\\*\\amsi.dll",
    "?:\\Windows\\SoftwareDistribution\\Download\\*",
    "?:\\Windows\\WinSxS\\*\\amsi.dll", 
    "?:\\Windows\\servicing\\*\\amsi.dll",
    "\\\\?\\Volume{*}\\Windows\\WinSxS\\*\\amsi.dll", 
    "\\\\?\\Volume{*}\\Windows\\system32\\amsi.dll", 
    "\\\\?\\Volume{*}\\Windows\\syswow64\\amsi.dll",

    /* Crowdstrike specific exclusion as it uses NT Object paths */
    "\\Device\\HarddiskVolume*\\Windows\\system32\\amsi.dll", 
    "\\Device\\HarddiskVolume*\\Windows\\syswow64\\amsi.dll", 
    "\\Device\\HarddiskVolume*\\Windows\\WinSxS\\*\\amsi.dll",
    "\\Device\\HarddiskVolume*\\$SysReset\\CloudImage\\Package_for_RollupFix*\\amsi.dll",
    "\\Device\\HarddiskVolume*\\$WINDOWS.~BT\\*\\amsi.dll", 
    "\\Device\\HarddiskVolume*\\Windows\\SoftwareDistribution\\Download\\*\\amsi.dll", 
    "\\Device\\HarddiskVolume*\\Windows\\CbsTemp\\*\\amsi.dll", 
    "\\Device\\HarddiskVolume*\\Windows\\servicing\\*\\amsi.dll"
  ) 

Install detection rules in Elastic Security

Detect Suspicious Antimalware Scan Interface DLL in the Elastic Security detection engine by installing this rule into your Elastic Stack.

To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(opens in a new tab or window).