IMPORTANT: No additional bug fixes or documentation updates
will be released for this version. For the latest information, see the
current release documentation.
Microsoft Exchange Server UM Writing Suspicious Files
editMicrosoft Exchange Server UM Writing Suspicious Files
editIdentifies 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.*
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: 1
Added (Elastic Stack release): 7.12.0
Rule authors: Elastic, Austin Songer
Rule license: Elastic License v2
Potential false positives
editFiles generated during installation will generate a lot of noise, so the rule should only be enabled after the fact.
Rule query
editfile where event.type == "creation" and process.parent.name : ("UMWorkerProcess.exe", "umservice.exe") and file.extension : ("php", "jsp", "js", "aspx", "asmx", "asax", "cfm", "shtml") and ( file.path : ("C:\\inetpub\\wwwroot\\aspnet_client\\*", "C:\\*\\FrontEnd\\HttpProxy\\owa\\auth\\*") or (file.path : "C:\\*\\FrontEnd\\HttpProxy\\ecp\\auth\\*" and not file.name : "TimeoutLogoff.aspx") )
Threat mapping
editFramework: MITRE ATT&CKTM
-
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/