Microsoft Exchange Server UM Writing Suspicious Files

  1[metadata]
  2creation_date = "2021/03/04"
  3integration = ["endpoint", "windows", "m365_defender", "sentinel_one_cloud_funnel"]
  4maturity = "production"
  5updated_date = "2024/10/15"
  6min_stack_version = "8.14.0"
  7min_stack_comments = "Breaking change at 8.14.0 for the Windows Integration."
  8
  9[rule]
 10author = ["Elastic", "Austin Songer"]
 11description = """
 12Identifies suspicious files being written by the Microsoft Exchange Server Unified Messaging (UM) service. This activity
 13has been observed exploiting CVE-2021-26858.
 14"""
 15false_positives = [
 16    """
 17    Files generated during installation will generate a lot of noise, so the rule should only be enabled after the fact.
 18    """,
 19    """
 20    This rule was tuned using the following baseline:
 21    https://raw.githubusercontent.com/microsoft/CSS-Exchange/main/Security/Baselines/baseline_15.2.792.5.csv from
 22    Microsoft. Depending on version, consult https://github.com/microsoft/CSS-Exchange/tree/main/Security/Baselines to
 23    help determine normalcy.
 24    """,
 25]
 26from = "now-9m"
 27index = ["winlogbeat-*", "logs-endpoint.events.file-*", "logs-windows.sysmon_operational-*", "endgame-*", "logs-m365_defender.event-*", "logs-sentinel_one_cloud_funnel.*"]
 28language = "eql"
 29license = "Elastic License v2"
 30name = "Microsoft Exchange Server UM Writing Suspicious Files"
 31note = """## Triage and analysis
 32
 33Positive hits can be checked against the established Microsoft [baselines](https://github.com/microsoft/CSS-Exchange/tree/main/Security/Baselines).
 34
 35Microsoft highly recommends that the best course of action is patching, but this may not protect already compromised systems
 36from existing intrusions. Other tools for detecting and mitigating can be found within their Exchange support
 37[repository](https://github.com/microsoft/CSS-Exchange/tree/main/Security)
 38"""
 39references = [
 40    "https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers",
 41    "https://www.volexity.com/blog/2021/03/02/active-exploitation-of-microsoft-exchange-zero-day-vulnerabilities",
 42]
 43risk_score = 47
 44rule_id = "6cd1779c-560f-4b68-a8f1-11009b27fe63"
 45severity = "medium"
 46tags = [
 47    "Domain: Endpoint",
 48    "OS: Windows",
 49    "Use Case: Threat Detection",
 50    "Tactic: Initial Access",
 51    "Tactic: Lateral Movement",
 52    "Data Source: Elastic Endgame",
 53    "Use Case: Vulnerability",
 54    "Data Source: Elastic Defend",
 55    "Data Source: Sysmon",
 56    "Data Source: Microsoft Defender for Endpoint",
 57    "Data Source: SentinelOne",
 58]
 59timestamp_override = "event.ingested"
 60type = "eql"
 61
 62query = '''
 63file where host.os.type == "windows" and event.type == "creation" and
 64  process.name : ("UMWorkerProcess.exe", "umservice.exe") and
 65  file.extension : ("php", "jsp", "js", "aspx", "asmx", "asax", "cfm", "shtml") and
 66  (
 67    file.path : "?:\\inetpub\\wwwroot\\aspnet_client\\*" or
 68
 69    (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\owa\\auth\\*" and
 70       not (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\owa\\auth\\version\\*" or
 71            file.name : ("errorFE.aspx", "expiredpassword.aspx", "frowny.aspx", "GetIdToken.htm", "logoff.aspx",
 72                        "logon.aspx", "OutlookCN.aspx", "RedirSuiteServiceProxy.aspx", "signout.aspx"))) or
 73
 74    (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\ecp\\auth\\*" and
 75       not file.name : "TimeoutLogoff.aspx")
 76  )
 77'''
 78
 79
 80[[rule.threat]]
 81framework = "MITRE ATT&CK"
 82[[rule.threat.technique]]
 83id = "T1190"
 84name = "Exploit Public-Facing Application"
 85reference = "https://attack.mitre.org/techniques/T1190/"
 86
 87
 88[rule.threat.tactic]
 89id = "TA0001"
 90name = "Initial Access"
 91reference = "https://attack.mitre.org/tactics/TA0001/"
 92[[rule.threat]]
 93framework = "MITRE ATT&CK"
 94[[rule.threat.technique]]
 95id = "T1210"
 96name = "Exploitation of Remote Services"
 97reference = "https://attack.mitre.org/techniques/T1210/"
 98
 99
100[rule.threat.tactic]
101id = "TA0008"
102name = "Lateral Movement"
103reference = "https://attack.mitre.org/tactics/TA0008/"