Microsoft Exchange Server UM Writing Suspicious Files

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Microsoft Exchange Server UM Writing Suspicious Files

Identifies suspicious files being written by the Microsoft Exchange Server Unified Messaging (UM) service. This activity has been observed exploiting CVE-2021-26858.

Rule type: eql

Rule indices:

winlogbeat-*
logs-endpoint.events.file-*
logs-windows.sysmon_operational-*
endgame-*
logs-m365_defender.event-*
logs-sentinel_one_cloud_funnel.*

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
Data Source: Sysmon
Data Source: Microsoft Defender XDR
Data Source: SentinelOne
Resources: Investigation Guide

Version: 314

Rule authors:

Elastic
Austin Songer

Rule license: Elastic License v2

Investigation guide

edit

Triage and analysis

Positive hits can be checked against the established Microsoft baselines.

Microsoft highly recommends that the best course of action is patching, but this may not protect already compromised systems from existing intrusions. Other tools for detecting and mitigating can be found within their Exchange support repository

Setup

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Setup

This rule is designed for data generated by Elastic Defend, which provides native endpoint detection and response, along with event enrichments designed to work with our detection rules.

Setup instructions: https://ela.st/install-elastic-defend

Additional data sources

This rule also supports the following third-party data sources. For setup instructions, refer to the links below:

Rule query

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file where host.os.type == "windows" and event.type == "creation" and
  process.name : ("UMWorkerProcess.exe", "umservice.exe") and
  file.extension : ("php", "jsp", "js", "aspx", "asmx", "asax", "cfm", "shtml") and
  (
    file.path : "?:\\inetpub\\wwwroot\\aspnet_client\\*" or

    (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\owa\\auth\\*" and
       not (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\owa\\auth\\version\\*" or
            file.name : ("errorFE.aspx", "expiredpassword.aspx", "frowny.aspx", "GetIdToken.htm", "logoff.aspx",
                        "logon.aspx", "OutlookCN.aspx", "RedirSuiteServiceProxy.aspx", "signout.aspx"))) or

    (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\ecp\\auth\\*" and
       not file.name : "TimeoutLogoff.aspx")
  )

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/
Tactic:
- Name: Lateral Movement
- ID: TA0008
- Reference URL: https://attack.mitre.org/tactics/TA0008/
Technique:
- Name: Exploitation of Remote Services
- ID: T1210
- Reference URL: https://attack.mitre.org/techniques/T1210/
Tactic:
- Name: Persistence
- ID: TA0003
- Reference URL: https://attack.mitre.org/tactics/TA0003/
Technique:
- Name: Server Software Component
- ID: T1505
- Reference URL: https://attack.mitre.org/techniques/T1505/
Sub-technique:
- Name: Web Shell
- ID: T1505.003
- Reference URL: https://attack.mitre.org/techniques/T1505/003/

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