Microsoft Exchange Server UM Spawning Suspicious Processes

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Microsoft Exchange Server UM Spawning Suspicious Processes

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Identifies suspicious processes being spawned by the Microsoft Exchange Server Unified Messaging (UM) service. This activity has been observed exploiting CVE-2021-26857.

Rule type: eql

Rule indices:

  • logs-endpoint.events.process-*
  • winlogbeat-*
  • logs-windows.*
  • endgame-*
  • logs-system.security*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Endpoint
  • OS: Windows
  • Use Case: Threat Detection
  • Tactic: Initial Access
  • Tactic: Lateral Movement
  • Data Source: Elastic Endgame
  • Use Case: Vulnerability
  • Data Source: Elastic Defend

Version: 109

Rule authors:

  • Elastic
  • Austin Songer

Rule license: Elastic License v2

Setup

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Setup

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define event.ingested and default fallback for EQL rules was not added until version 8.2. Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate event.ingested to @timestamp. For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html

Rule query

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process where host.os.type == "windows" and event.type == "start" and
  process.parent.name : ("UMService.exe", "UMWorkerProcess.exe") and
    not process.executable :
              ("?:\\Windows\\System32\\werfault.exe",
               "?:\\Windows\\System32\\wermgr.exe",
               "?:\\Program Files\\Microsoft\\Exchange Server\\V??\\Bin\\UMWorkerProcess.exe",
               "?:\\Program Files\\Microsoft\\Exchange Server\\Bin\\UMWorkerProcess.exe",
               "D:\\Exchange 2016\\Bin\\UMWorkerProcess.exe",
               "E:\\ExchangeServer\\Bin\\UMWorkerProcess.exe",
               "D:\\Exchange\\Bin\\UMWorkerProcess.exe",
               "D:\\Exchange Server\\Bin\\UMWorkerProcess.exe",
               "E:\\Exchange Server\\V15\\Bin\\UMWorkerProcess.exe")

Framework: MITRE ATT&CKTM