Network Connection via Compiled HTML File

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Compiled HTML files (.chm) are commonly distributed as part of the Microsoft HTML Help system. Adversaries may conceal malicious code in a CHM file and deliver it to a victim for execution. CHM content is loaded by the HTML Help executable program (hh.exe).

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-endpoint.events.*

Severity: low

Risk score: 21

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Execution

Version: 5 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 7.10.0

Rule authors: Elastic

Rule license: Elastic License

Rule query

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sequence by process.entity_id [process where process.name : "hh.exe"
and event.type == "start"] [network where process.name : "hh.exe"
and not cidrmatch(destination.ip, "10.0.0.0/8", "172.16.0.0/12",
"192.168.0.0/16")]

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 5 (7.10.0 release)
  • Updated query, changed from:

    event.category:network and event.type:connection and
    process.name:hh.exe and not destination.ip:(10.0.0.0/8 or
    172.16.0.0/12 or 192.168.0.0/16)
Version 4 (7.9.1 release)
  • Formatting only
Version 3 (7.9.0 release)
  • Updated query, changed from:

    process.name:hh.exe and event.action:"Network connection detected
    (rule: NetworkConnect)" and not destination.ip:(10.0.0.0/8 or
    172.16.0.0/12 or 192.168.0.0/16)
Version 2 (7.7.0 release)
  • Updated query, changed from:

    process.name:hh.exe and event.action:"Network connection detected
    (rule: NetworkConnect)" and not destination.ip:10.0.0.0/8 and not
    destination.ip:172.16.0.0/12 and not destination.ip:192.168.0.0/16