Microsoft Exchange Server UM Spawning Suspicious Processes

Microsoft Exchange Server UM Spawning Suspicious Processesedit

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:

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

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



  • 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



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 -

Rule queryedit

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