IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.
« Windows Script Interpreter Executing Process via WMI Microsoft Exchange Server UM Spawning Suspicious Processes »
Elastic Docs ›Elastic Security Solution [8.10] ›Downloadable rule update v8.10.2

Microsoft Exchange Server UM Writing Suspicious Files

edit

Microsoft Exchange Server UM Writing Suspicious Files

edit

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.*
  • 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

References:

Tags:

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

Version: 104

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](https://github.com/microsoft/CSS-Exchange/tree/main/Security/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](https://github.com/microsoft/CSS-Exchange/tree/main/Security)

Rule query

edit
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&CKTM

« Windows Script Interpreter Executing Process via WMI Microsoft Exchange Server UM Spawning Suspicious Processes »