Suspicious Antimalware Scan Interface DLL

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.

Rule type: eql

Rule indices:

• winlogbeat-*
• logs-endpoint.events.*
• logs-windows.*
• endgame-*

Severity: high

Risk score: 73

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

• https://github.com/S3cur3Th1sSh1t/Amsi-Bypass-Powershell

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Defense Evasion
• Elastic Endgame

Version: 1

Rule authors:

• Elastic

Rule license: Elastic License v2

file where event.action != "deletion" and file.path != null and
 file.name : ("amsi.dll", "amsi") and not file.path : ("?:\\Windows\\system32\\amsi.dll", "?:\\Windows\\Syswow64\\amsi.dll")

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Defense Evasion
  • ID: TA0005
  • Reference URL: https://attack.mitre.org/tactics/TA0005/

• Technique:

  • Name: Impair Defenses
  • ID: T1562
  • Reference URL: https://attack.mitre.org/techniques/T1562/

• Sub-technique:

  • Name: Disable or Modify Tools
  • ID: T1562.001
  • Reference URL: https://attack.mitre.org/techniques/T1562/001/

• Technique:

  • Name: Hijack Execution Flow
  • ID: T1574
  • Reference URL: https://attack.mitre.org/techniques/T1574/

• Sub-technique:

  • Name: DLL Search Order Hijacking
  • ID: T1574.001
  • Reference URL: https://attack.mitre.org/techniques/T1574/001/