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.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 for Endpoint
- Data Source: SentinelOne
Version: 208
Rule authors:
- Elastic
- Austin Songer
Rule license: Elastic License v2
Investigation guide
editTriage 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
Rule query
editfile 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
-
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/