New ActiveSyncAllowedDeviceID Added via PowerShell

Elastic Stack Serverless Security

Identifies the use of the Exchange PowerShell cmdlet, Set-CASMailbox, to add a new ActiveSync allowed device. Adversaries may target user email to collect sensitive information.

Rule type: eql

Rule indices:

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

Severity: medium

Risk score: 47

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://www.volexity.com/blog/2020/12/14/dark-halo-leverages-solarwinds-compromise-to-breach-organizations/
• https://docs.microsoft.com/en-us/powershell/module/exchange/set-casmailbox?view=exchange-ps

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Persistence

Version: 102

Rule authors:

• Elastic

Rule license: Elastic License v2

process where event.type == "start" and
  process.name: ("powershell.exe", "pwsh.exe", "powershell_ise.exe") and process.args : "Set-CASMailbox*ActiveSyncAllowedDeviceIDs*"

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Persistence
  • ID: TA0003
  • Reference URL: https://attack.mitre.org/tactics/TA0003/

• Technique:

  • Name: Account Manipulation
  • ID: T1098
  • Reference URL: https://attack.mitre.org/techniques/T1098/

• Sub-technique:

  • Name: Additional Email Delegate Permissions
  • ID: T1098.002
  • Reference URL: https://attack.mitre.org/techniques/T1098/002/