Microsoft Exchange Server UM Writing Suspicious Files

  1[metadata]
  2creation_date = "2021/03/04"
  3integration = ["endpoint", "windows"]
  4maturity = "production"
  5min_stack_comments = "New fields added: required_fields, related_integrations, setup"
  6min_stack_version = "8.3.0"
  7updated_date = "2024/03/28"
  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-*"]
 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"
 45setup = """## Setup
 46
 47If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
 48events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
 49Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
 50`event.ingested` to @timestamp.
 51For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
 52"""
 53severity = "medium"
 54tags = ["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"]
 55timestamp_override = "event.ingested"
 56type = "eql"
 57
 58query = '''
 59file where host.os.type == "windows" and event.type == "creation" and
 60  process.name : ("UMWorkerProcess.exe", "umservice.exe") and
 61  file.extension : ("php", "jsp", "js", "aspx", "asmx", "asax", "cfm", "shtml") and
 62  (
 63    file.path : "?:\\inetpub\\wwwroot\\aspnet_client\\*" or
 64
 65    (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\owa\\auth\\*" and
 66       not (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\owa\\auth\\version\\*" or
 67            file.name : ("errorFE.aspx", "expiredpassword.aspx", "frowny.aspx", "GetIdToken.htm", "logoff.aspx",
 68                        "logon.aspx", "OutlookCN.aspx", "RedirSuiteServiceProxy.aspx", "signout.aspx"))) or
 69
 70    (file.path : "?:\\*\\Microsoft\\Exchange Server*\\FrontEnd\\HttpProxy\\ecp\\auth\\*" and
 71       not file.name : "TimeoutLogoff.aspx")
 72  )
 73'''
 74
 75
 76[[rule.threat]]
 77framework = "MITRE ATT&CK"
 78[[rule.threat.technique]]
 79id = "T1190"
 80name = "Exploit Public-Facing Application"
 81reference = "https://attack.mitre.org/techniques/T1190/"
 82
 83
 84[rule.threat.tactic]
 85id = "TA0001"
 86name = "Initial Access"
 87reference = "https://attack.mitre.org/tactics/TA0001/"
 88
 89
 90[[rule.threat]]
 91framework = "MITRE ATT&CK"
 92[[rule.threat.technique]]
 93id = "T1210"
 94name = "Exploitation of Remote Services"
 95reference = "https://attack.mitre.org/techniques/T1210/"
 96
 97
 98[rule.threat.tactic]
 99id = "TA0008"
100name = "Lateral Movement"
101reference = "https://attack.mitre.org/tactics/TA0008/"