IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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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.*
winlogbeat-*
logs-windows.*

Severity: medium

Risk score: 47

Runs every: 5 minutes

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

Maximum alerts per execution: 100

References:

Tags:

Elastic
Host
Windows
Threat Detection
Initial Access

Version: 4 (version history)

Added (Elastic Stack release): 7.12.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic, Austin Songer

Rule license: Elastic License v2

Potential false positives

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Legitimate processes may be spawned from the Microsoft Exchange Server Unified Messaging (UM) service. If known processes are causing false positives, they can be exempted from the rule.

Investigation guide

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Rule query

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process where 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",
"D:\\Exchange 2016\\Bin\\UMWorkerProcess.exe",
"E:\\ExchangeServer\\Bin\\UMWorkerProcess.exe")

Threat mapping

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Framework: MITRE ATT&CK^TM

Tactic:
- Name: Initial Access
- ID: TA0001
- Reference URL: https://attack.mitre.org/tactics/TA0001/
Technique:
- Name: Exploit Public-Facing Application
- ID: T1190
- Reference URL: https://attack.mitre.org/techniques/T1190/

Rule version history

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Version 4 (8.4.0 release)

Updated query, changed from:

process where event.type == "start" and process.parent.name :
("UMService.exe", "UMWorkerProcess.exe") and not process.name :
("werfault.exe", "wermgr.exe")

Version 2 (8.2.0 release)

Formatting only

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